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<li><a class="reference internal" href="#">4. Using Python on Windows</a><ul>
<li><a class="reference internal" href="#the-full-installer">4.1. The full installer</a><ul>
<li><a class="reference internal" href="#installation-steps">4.1.1. Installation steps</a></li>
<li><a class="reference internal" href="#removing-the-max-path-limitation">4.1.2. Removing the MAX_PATH Limitation</a></li>
<li><a class="reference internal" href="#installing-without-ui">4.1.3. Installing Without UI</a></li>
<li><a class="reference internal" href="#installing-without-downloading">4.1.4. Installing Without Downloading</a></li>
<li><a class="reference internal" href="#modifying-an-install">4.1.5. Modifying an install</a></li>
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<li><a class="reference internal" href="#the-microsoft-store-package">4.2. The Microsoft Store package</a><ul>
<li><a class="reference internal" href="#known-issues">4.2.1. Known issues</a><ul>
<li><a class="reference internal" href="#redirection-of-local-data-registry-and-temporary-paths">4.2.1.1. Redirection of local data, registry, and temporary paths</a></li>
</ul>
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</li>
<li><a class="reference internal" href="#the-nuget-org-packages">4.3. The nuget.org packages</a></li>
<li><a class="reference internal" href="#the-embeddable-package">4.4. The embeddable package</a><ul>
<li><a class="reference internal" href="#python-application">4.4.1. Python Application</a></li>
<li><a class="reference internal" href="#embedding-python">4.4.2. Embedding Python</a></li>
</ul>
</li>
<li><a class="reference internal" href="#alternative-bundles">4.5. Alternative bundles</a></li>
<li><a class="reference internal" href="#configuring-python">4.6. Configuring Python</a><ul>
<li><a class="reference internal" href="#excursus-setting-environment-variables">4.6.1. Excursus: Setting environment variables</a></li>
<li><a class="reference internal" href="#finding-the-python-executable">4.6.2. Finding the Python executable</a></li>
</ul>
</li>
<li><a class="reference internal" href="#utf-8-mode">4.7. UTF-8 mode</a></li>
<li><a class="reference internal" href="#python-launcher-for-windows">4.8. Python Launcher for Windows</a><ul>
<li><a class="reference internal" href="#getting-started">4.8.1. Getting started</a><ul>
<li><a class="reference internal" href="#from-the-command-line">4.8.1.1. From the command-line</a></li>
<li><a class="reference internal" href="#virtual-environments">4.8.1.2. Virtual environments</a></li>
<li><a class="reference internal" href="#from-a-script">4.8.1.3. From a script</a></li>
<li><a class="reference internal" href="#from-file-associations">4.8.1.4. From file associations</a></li>
</ul>
</li>
<li><a class="reference internal" href="#shebang-lines">4.8.2. Shebang Lines</a></li>
<li><a class="reference internal" href="#arguments-in-shebang-lines">4.8.3. Arguments in shebang lines</a></li>
<li><a class="reference internal" href="#customization">4.8.4. Customization</a><ul>
<li><a class="reference internal" href="#customization-via-ini-files">4.8.4.1. Customization via INI files</a></li>
<li><a class="reference internal" href="#customizing-default-python-versions">4.8.4.2. Customizing default Python versions</a></li>
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<li><a class="reference internal" href="#diagnostics">4.8.5. Diagnostics</a></li>
<li><a class="reference internal" href="#dry-run">4.8.6. Dry Run</a></li>
<li><a class="reference internal" href="#install-on-demand">4.8.7. Install on demand</a></li>
<li><a class="reference internal" href="#return-codes">4.8.8. Return codes</a></li>
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<li><a class="reference internal" href="#finding-modules">4.9. Finding modules</a></li>
<li><a class="reference internal" href="#additional-modules">4.10. Additional modules</a><ul>
<li><a class="reference internal" href="#pywin32">4.10.1. PyWin32</a></li>
<li><a class="reference internal" href="#cx-freeze">4.10.2. cx_Freeze</a></li>
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<li><a class="reference internal" href="#compiling-python-on-windows">4.11. Compiling Python on Windows</a></li>
<li><a class="reference internal" href="#other-platforms">4.12. Other Platforms</a></li>
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  <section id="using-python-on-windows">
<span id="using-on-windows"></span><h1><span class="section-number">4. </span>Using Python on Windows<a class="headerlink" href="#using-python-on-windows" title="Permalink to this headline">¶</a></h1>
<p>This document aims to give an overview of Windows-specific behaviour you should
know about when using Python on Microsoft Windows.</p>
<p>Unlike most Unix systems and services, Windows does not include a system
supported installation of Python. To make Python available, the CPython team
has compiled Windows installers (MSI packages) with every <a class="reference external" href="https://www.python.org/download/releases/">release</a> for many years. These installers
are primarily intended to add a per-user installation of Python, with the
core interpreter and library being used by a single user. The installer is also
able to install for all users of a single machine, and a separate ZIP file is
available for application-local distributions.</p>
<p>As specified in <span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0011/"><strong>PEP 11</strong></a>, a Python release only supports a Windows platform
while Microsoft considers the platform under extended support. This means that
Python 3.12 supports Windows 8.1 and newer. If you require Windows 7
support, please install Python 3.8.</p>
<p>There are a number of different installers available for Windows, each with
certain benefits and downsides.</p>
<p><a class="reference internal" href="#windows-full"><span class="std std-ref">The full installer</span></a> contains all components and is the best option for
developers using Python for any kind of project.</p>
<p><a class="reference internal" href="#windows-store"><span class="std std-ref">The Microsoft Store package</span></a> is a simple installation of Python that is suitable for
running scripts and packages, and using IDLE or other development environments.
It requires Windows 10 and above, but can be safely installed without corrupting other
programs. It also provides many convenient commands for launching Python and
its tools.</p>
<p><a class="reference internal" href="#windows-nuget"><span class="std std-ref">The nuget.org packages</span></a> are lightweight installations intended for continuous
integration systems. It can be used to build Python packages or run scripts,
but is not updateable and has no user interface tools.</p>
<p><a class="reference internal" href="#windows-embeddable"><span class="std std-ref">The embeddable package</span></a> is a minimal package of Python suitable for
embedding into a larger application.</p>
<section id="the-full-installer">
<span id="windows-full"></span><h2><span class="section-number">4.1. </span>The full installer<a class="headerlink" href="#the-full-installer" title="Permalink to this headline">¶</a></h2>
<section id="installation-steps">
<h3><span class="section-number">4.1.1. </span>Installation steps<a class="headerlink" href="#installation-steps" title="Permalink to this headline">¶</a></h3>
<p>Four Python 3.12 installers are available for download - two each for the
32-bit and 64-bit versions of the interpreter. The <em>web installer</em> is a small
initial download, and it will automatically download the required components as
necessary. The <em>offline installer</em> includes the components necessary for a
default installation and only requires an internet connection for optional
features. See <a class="reference internal" href="#install-layout-option"><span class="std std-ref">Installing Without Downloading</span></a> for other ways to avoid downloading
during installation.</p>
<p>After starting the installer, one of two options may be selected:</p>
<img alt="../_images/win_installer.png" src="../_images/win_installer.png" />
<p>If you select “Install Now”:</p>
<ul class="simple">
<li><p>You will <em>not</em> need to be an administrator (unless a system update for the
C Runtime Library is required or you install the <a class="reference internal" href="#launcher"><span class="std std-ref">Python Launcher for Windows</span></a> for all
users)</p></li>
<li><p>Python will be installed into your user directory</p></li>
<li><p>The <a class="reference internal" href="#launcher"><span class="std std-ref">Python Launcher for Windows</span></a> will be installed according to the option at the bottom
of the first page</p></li>
<li><p>The standard library, test suite, launcher and pip will be installed</p></li>
<li><p>If selected, the install directory will be added to your <span class="target" id="index-1"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code></p></li>
<li><p>Shortcuts will only be visible for the current user</p></li>
</ul>
<p>Selecting “Customize installation” will allow you to select the features to
install, the installation location and other options or post-install actions.
To install debugging symbols or binaries, you will need to use this option.</p>
<p>To perform an all-users installation, you should select “Customize
installation”. In this case:</p>
<ul class="simple">
<li><p>You may be required to provide administrative credentials or approval</p></li>
<li><p>Python will be installed into the Program Files directory</p></li>
<li><p>The <a class="reference internal" href="#launcher"><span class="std std-ref">Python Launcher for Windows</span></a> will be installed into the Windows directory</p></li>
<li><p>Optional features may be selected during installation</p></li>
<li><p>The standard library can be pre-compiled to bytecode</p></li>
<li><p>If selected, the install directory will be added to the system <span class="target" id="index-2"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code></p></li>
<li><p>Shortcuts are available for all users</p></li>
</ul>
</section>
<section id="removing-the-max-path-limitation">
<span id="max-path"></span><h3><span class="section-number">4.1.2. </span>Removing the MAX_PATH Limitation<a class="headerlink" href="#removing-the-max-path-limitation" title="Permalink to this headline">¶</a></h3>
<p>Windows historically has limited path lengths to 260 characters. This meant that
paths longer than this would not resolve and errors would result.</p>
<p>In the latest versions of Windows, this limitation can be expanded to
approximately 32,000 characters. Your administrator will need to activate the
“Enable Win32 long paths” group policy, or set <code class="docutils literal notranslate"><span class="pre">LongPathsEnabled</span></code> to <code class="docutils literal notranslate"><span class="pre">1</span></code>
in the registry key
<code class="docutils literal notranslate"><span class="pre">HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem</span></code>.</p>
<p>This allows the <a class="reference internal" href="../library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> function, the <a class="reference internal" href="../library/os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module and most other
path functionality to accept and return paths longer than 260 characters.</p>
<p>After changing the above option, no further configuration is required.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.6: </span>Support for long paths was enabled in Python.</p>
</div>
</section>
<section id="installing-without-ui">
<span id="install-quiet-option"></span><h3><span class="section-number">4.1.3. </span>Installing Without UI<a class="headerlink" href="#installing-without-ui" title="Permalink to this headline">¶</a></h3>
<p>All of the options available in the installer UI can also be specified from the
command line, allowing scripted installers to replicate an installation on many
machines without user interaction.  These options may also be set without
suppressing the UI in order to change some of the defaults.</p>
<p>The following options (found by executing the installer with <code class="docutils literal notranslate"><span class="pre">/?</span></code>) can be
passed into the installer:</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 27%" />
<col style="width: 73%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Name</p></th>
<th class="head"><p>Description</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>/passive</p></td>
<td><p>to display progress without requiring user interaction</p></td>
</tr>
<tr class="row-odd"><td><p>/quiet</p></td>
<td><p>to install/uninstall without displaying any UI</p></td>
</tr>
<tr class="row-even"><td><p>/simple</p></td>
<td><p>to prevent user customization</p></td>
</tr>
<tr class="row-odd"><td><p>/uninstall</p></td>
<td><p>to remove Python (without confirmation)</p></td>
</tr>
<tr class="row-even"><td><p>/layout [directory]</p></td>
<td><p>to pre-download all components</p></td>
</tr>
<tr class="row-odd"><td><p>/log [filename]</p></td>
<td><p>to specify log files location</p></td>
</tr>
</tbody>
</table>
<p>All other options are passed as <code class="docutils literal notranslate"><span class="pre">name=value</span></code>, where the value is usually
<code class="docutils literal notranslate"><span class="pre">0</span></code> to disable a feature, <code class="docutils literal notranslate"><span class="pre">1</span></code> to enable a feature, or a path. The full list
of available options is shown below.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 30%" />
<col style="width: 42%" />
<col style="width: 29%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Name</p></th>
<th class="head"><p>Description</p></th>
<th class="head"><p>Default</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>InstallAllUsers</p></td>
<td><p>Perform a system-wide installation.</p></td>
<td><p>0</p></td>
</tr>
<tr class="row-odd"><td><p>TargetDir</p></td>
<td><p>The installation directory</p></td>
<td><p>Selected based on
InstallAllUsers</p></td>
</tr>
<tr class="row-even"><td><p>DefaultAllUsersTargetDir</p></td>
<td><p>The default installation directory
for all-user installs</p></td>
<td><p><code class="file docutils literal notranslate"><span class="pre">%ProgramFiles%\Python</span> <span class="pre">X.Y</span></code> or <code class="file docutils literal notranslate"><span class="pre">%ProgramFiles(x86)%\Python</span> <span class="pre">X.Y</span></code></p></td>
</tr>
<tr class="row-odd"><td><p>DefaultJustForMeTargetDir</p></td>
<td><p>The default install directory for
just-for-me installs</p></td>
<td><p><code class="file docutils literal notranslate"><span class="pre">%LocalAppData%\Programs\Python\PythonXY</span></code> or
<code class="file docutils literal notranslate"><span class="pre">%LocalAppData%\Programs\Python\PythonXY-32</span></code> or
<code class="file docutils literal notranslate"><span class="pre">%LocalAppData%\Programs\Python\PythonXY-64</span></code></p></td>
</tr>
<tr class="row-even"><td><p>DefaultCustomTargetDir</p></td>
<td><p>The default custom install directory
displayed in the UI</p></td>
<td><p>(empty)</p></td>
</tr>
<tr class="row-odd"><td><p>AssociateFiles</p></td>
<td><p>Create file associations if the
launcher is also installed.</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-even"><td><p>CompileAll</p></td>
<td><p>Compile all <code class="docutils literal notranslate"><span class="pre">.py</span></code> files to
<code class="docutils literal notranslate"><span class="pre">.pyc</span></code>.</p></td>
<td><p>0</p></td>
</tr>
<tr class="row-odd"><td><p>PrependPath</p></td>
<td><p>Prepend install and Scripts
directories  to <span class="target" id="index-3"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code> and
add <code class="docutils literal notranslate"><span class="pre">.PY</span></code> to <span class="target" id="index-4"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATHEXT</span></code></p></td>
<td><p>0</p></td>
</tr>
<tr class="row-even"><td><p>AppendPath</p></td>
<td><p>Append install and Scripts
directories  to <span class="target" id="index-5"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code> and
add <code class="docutils literal notranslate"><span class="pre">.PY</span></code> to <span class="target" id="index-6"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATHEXT</span></code></p></td>
<td><p>0</p></td>
</tr>
<tr class="row-odd"><td><p>Shortcuts</p></td>
<td><p>Create shortcuts for the interpreter,
documentation and IDLE if installed.</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-even"><td><p>Include_doc</p></td>
<td><p>Install Python manual</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-odd"><td><p>Include_debug</p></td>
<td><p>Install debug binaries</p></td>
<td><p>0</p></td>
</tr>
<tr class="row-even"><td><p>Include_dev</p></td>
<td><p>Install developer headers and
libraries. Omitting this may lead to
an unusable installation.</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-odd"><td><p>Include_exe</p></td>
<td><p>Install <code class="file docutils literal notranslate"><span class="pre">python.exe</span></code> and
related files. Omitting this may
lead to an unusable installation.</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-even"><td><p>Include_launcher</p></td>
<td><p>Install <a class="reference internal" href="#launcher"><span class="std std-ref">Python Launcher for Windows</span></a>.</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-odd"><td><p>InstallLauncherAllUsers</p></td>
<td><p>Installs the launcher for all
users. Also requires
<code class="docutils literal notranslate"><span class="pre">Include_launcher</span></code> to be set to 1</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-even"><td><p>Include_lib</p></td>
<td><p>Install standard library and
extension modules. Omitting this may
lead to an unusable installation.</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-odd"><td><p>Include_pip</p></td>
<td><p>Install bundled pip and setuptools</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-even"><td><p>Include_symbols</p></td>
<td><p>Install debugging symbols (<code class="docutils literal notranslate"><span class="pre">*.pdb</span></code>)</p></td>
<td><p>0</p></td>
</tr>
<tr class="row-odd"><td><p>Include_tcltk</p></td>
<td><p>Install Tcl/Tk support and IDLE</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-even"><td><p>Include_test</p></td>
<td><p>Install standard library test suite</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-odd"><td><p>Include_tools</p></td>
<td><p>Install utility scripts</p></td>
<td><p>1</p></td>
</tr>
<tr class="row-even"><td><p>LauncherOnly</p></td>
<td><p>Only installs the launcher. This
will override most other options.</p></td>
<td><p>0</p></td>
</tr>
<tr class="row-odd"><td><p>SimpleInstall</p></td>
<td><p>Disable most install UI</p></td>
<td><p>0</p></td>
</tr>
<tr class="row-even"><td><p>SimpleInstallDescription</p></td>
<td><p>A custom message to display when the
simplified install UI is used.</p></td>
<td><p>(empty)</p></td>
</tr>
</tbody>
</table>
<p>For example, to silently install a default, system-wide Python installation,
you could use the following command (from an elevated command prompt):</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>python-3.9.0.exe /quiet InstallAllUsers=1 PrependPath=1 Include_test=0
</pre></div>
</div>
<p>To allow users to easily install a personal copy of Python without the test
suite, you could provide a shortcut with the following command. This will
display a simplified initial page and disallow customization:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>python-3.9.0.exe InstallAllUsers=0 Include_launcher=0 Include_test=0
    SimpleInstall=1 SimpleInstallDescription=&quot;Just for me, no test suite.&quot;
</pre></div>
</div>
<p>(Note that omitting the launcher also omits file associations, and is only
recommended for per-user installs when there is also a system-wide installation
that included the launcher.)</p>
<p>The options listed above can also be provided in a file named <code class="docutils literal notranslate"><span class="pre">unattend.xml</span></code>
alongside the executable. This file specifies a list of options and values.
When a value is provided as an attribute, it will be converted to a number if
possible. Values provided as element text are always left as strings. This
example file sets the same options as the previous example:</p>
<div class="highlight-xml notranslate"><div class="highlight"><pre><span></span><span class="nt">&lt;Options&gt;</span>
<span class="w">    </span><span class="nt">&lt;Option</span><span class="w"> </span><span class="na">Name=</span><span class="s">&quot;InstallAllUsers&quot;</span><span class="w"> </span><span class="na">Value=</span><span class="s">&quot;no&quot;</span><span class="w"> </span><span class="nt">/&gt;</span>
<span class="w">    </span><span class="nt">&lt;Option</span><span class="w"> </span><span class="na">Name=</span><span class="s">&quot;Include_launcher&quot;</span><span class="w"> </span><span class="na">Value=</span><span class="s">&quot;0&quot;</span><span class="w"> </span><span class="nt">/&gt;</span>
<span class="w">    </span><span class="nt">&lt;Option</span><span class="w"> </span><span class="na">Name=</span><span class="s">&quot;Include_test&quot;</span><span class="w"> </span><span class="na">Value=</span><span class="s">&quot;no&quot;</span><span class="w"> </span><span class="nt">/&gt;</span>
<span class="w">    </span><span class="nt">&lt;Option</span><span class="w"> </span><span class="na">Name=</span><span class="s">&quot;SimpleInstall&quot;</span><span class="w"> </span><span class="na">Value=</span><span class="s">&quot;yes&quot;</span><span class="w"> </span><span class="nt">/&gt;</span>
<span class="w">    </span><span class="nt">&lt;Option</span><span class="w"> </span><span class="na">Name=</span><span class="s">&quot;SimpleInstallDescription&quot;</span><span class="nt">&gt;</span>Just<span class="w"> </span>for<span class="w"> </span>me,<span class="w"> </span>no<span class="w"> </span>test<span class="w"> </span>suite<span class="nt">&lt;/Option&gt;</span>
<span class="nt">&lt;/Options&gt;</span>
</pre></div>
</div>
</section>
<section id="installing-without-downloading">
<span id="install-layout-option"></span><h3><span class="section-number">4.1.4. </span>Installing Without Downloading<a class="headerlink" href="#installing-without-downloading" title="Permalink to this headline">¶</a></h3>
<p>As some features of Python are not included in the initial installer download,
selecting those features may require an internet connection.  To avoid this
need, all possible components may be downloaded on-demand to create a complete
<em>layout</em> that will no longer require an internet connection regardless of the
selected features. Note that this download may be bigger than required, but
where a large number of installations are going to be performed it is very
useful to have a locally cached copy.</p>
<p>Execute the following command from Command Prompt to download all possible
required files.  Remember to substitute <code class="docutils literal notranslate"><span class="pre">python-3.9.0.exe</span></code> for the actual
name of your installer, and to create layouts in their own directories to
avoid collisions between files with the same name.</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>python-3.9.0.exe /layout [optional target directory]
</pre></div>
</div>
<p>You may also specify the <code class="docutils literal notranslate"><span class="pre">/quiet</span></code> option to hide the progress display.</p>
</section>
<section id="modifying-an-install">
<h3><span class="section-number">4.1.5. </span>Modifying an install<a class="headerlink" href="#modifying-an-install" title="Permalink to this headline">¶</a></h3>
<p>Once Python has been installed, you can add or remove features through the
Programs and Features tool that is part of Windows. Select the Python entry and
choose “Uninstall/Change” to open the installer in maintenance mode.</p>
<p>“Modify” allows you to add or remove features by modifying the checkboxes -
unchanged checkboxes will not install or remove anything. Some options cannot be
changed in this mode, such as the install directory; to modify these, you will
need to remove and then reinstall Python completely.</p>
<p>“Repair” will verify all the files that should be installed using the current
settings and replace any that have been removed or modified.</p>
<p>“Uninstall” will remove Python entirely, with the exception of the
<a class="reference internal" href="#launcher"><span class="std std-ref">Python Launcher for Windows</span></a>, which has its own entry in Programs and Features.</p>
</section>
</section>
<section id="the-microsoft-store-package">
<span id="windows-store"></span><h2><span class="section-number">4.2. </span>The Microsoft Store package<a class="headerlink" href="#the-microsoft-store-package" title="Permalink to this headline">¶</a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.2.</span></p>
</div>
<p>The Microsoft Store package is an easily installable Python interpreter that
is intended mainly for interactive use, for example, by students.</p>
<p>To install the package, ensure you have the latest Windows 10 updates and
search the Microsoft Store app for “Python 3.12”. Ensure that the app
you select is published by the Python Software Foundation, and install it.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Python will always be available for free on the Microsoft Store. If you
are asked to pay for it, you have not selected the correct package.</p>
</div>
<p>After installation, Python may be launched by finding it in Start.
Alternatively, it will be available from any Command Prompt or PowerShell
session by typing <code class="docutils literal notranslate"><span class="pre">python</span></code>. Further, pip and IDLE may be used by typing
<code class="docutils literal notranslate"><span class="pre">pip</span></code> or <code class="docutils literal notranslate"><span class="pre">idle</span></code>. IDLE can also be found in Start.</p>
<p>All three commands are also available with version number suffixes, for
example, as <code class="docutils literal notranslate"><span class="pre">python3.exe</span></code> and <code class="docutils literal notranslate"><span class="pre">python3.x.exe</span></code> as well as
<code class="docutils literal notranslate"><span class="pre">python.exe</span></code> (where <code class="docutils literal notranslate"><span class="pre">3.x</span></code> is the specific version you want to launch,
such as 3.12). Open “Manage App Execution Aliases” through Start to
select which version of Python is associated with each command. It is
recommended to make sure that <code class="docutils literal notranslate"><span class="pre">pip</span></code> and <code class="docutils literal notranslate"><span class="pre">idle</span></code> are consistent with
whichever version of <code class="docutils literal notranslate"><span class="pre">python</span></code> is selected.</p>
<p>Virtual environments can be created with <code class="docutils literal notranslate"><span class="pre">python</span> <span class="pre">-m</span> <span class="pre">venv</span></code> and activated
and used as normal.</p>
<p>If you have installed another version of Python and added it to your
<code class="docutils literal notranslate"><span class="pre">PATH</span></code> variable, it will be available as <code class="docutils literal notranslate"><span class="pre">python.exe</span></code> rather than the
one from the Microsoft Store. To access the new installation, use
<code class="docutils literal notranslate"><span class="pre">python3.exe</span></code> or <code class="docutils literal notranslate"><span class="pre">python3.x.exe</span></code>.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">py.exe</span></code> launcher will detect this Python installation, but will prefer
installations from the traditional installer.</p>
<p>To remove Python, open Settings and use Apps and Features, or else find
Python in Start and right-click to select Uninstall. Uninstalling will
remove all packages you installed directly into this Python installation, but
will not remove any virtual environments</p>
<section id="known-issues">
<h3><span class="section-number">4.2.1. </span>Known issues<a class="headerlink" href="#known-issues" title="Permalink to this headline">¶</a></h3>
<section id="redirection-of-local-data-registry-and-temporary-paths">
<h4><span class="section-number">4.2.1.1. </span>Redirection of local data, registry, and temporary paths<a class="headerlink" href="#redirection-of-local-data-registry-and-temporary-paths" title="Permalink to this headline">¶</a></h4>
<p>Because of restrictions on Microsoft Store apps, Python scripts may not have
full write access to shared locations such as <span class="target" id="index-7"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">TEMP</span></code> and the registry.
Instead, it will write to a private copy. If your scripts must modify the
shared locations, you will need to install the full installer.</p>
<p>At runtime, Python will use a private copy of well-known Windows folders and the registry.
For example, if the environment variable <span class="target" id="index-8"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">%APPDATA%</span></code> is <code class="file docutils literal notranslate"><span class="pre">c:\Users\&lt;user&gt;\AppData\</span></code>,
then when writing to <code class="file docutils literal notranslate"><span class="pre">C:\Users\&lt;user&gt;\AppData\Local</span></code> will write to
<code class="file docutils literal notranslate"><span class="pre">C:\Users\&lt;user&gt;\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\Local\</span></code>.</p>
<p>When reading files, Windows will return the file from the private folder, or if that does not exist, the
real Windows directory. For example reading <code class="file docutils literal notranslate"><span class="pre">C:\Windows\System32</span></code> returns the contents of <code class="file docutils literal notranslate"><span class="pre">C:\Windows\System32</span></code>
plus the contents of <code class="file docutils literal notranslate"><span class="pre">C:\Program</span> <span class="pre">Files\WindowsApps\package_name\VFS\SystemX86</span></code>.</p>
<p>You can find the real path of any existing file using <a class="reference internal" href="../library/os.path.html#os.path.realpath" title="os.path.realpath"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.path.realpath()</span></code></a>:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">os</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">test_file</span> <span class="o">=</span> <span class="s1">&#39;C:</span><span class="se">\\</span><span class="s1">Users</span><span class="se">\\</span><span class="s1">example</span><span class="se">\\</span><span class="s1">AppData</span><span class="se">\\</span><span class="s1">Local</span><span class="se">\\</span><span class="s1">test.txt&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">realpath</span><span class="p">(</span><span class="n">test_file</span><span class="p">)</span>
<span class="go">&#39;C:\\Users\\example\\AppData\\Local\\Packages\\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\\LocalCache\\Local\\test.txt&#39;</span>
</pre></div>
</div>
<p>When writing to the Windows Registry, the following behaviors exist:</p>
<ul class="simple">
<li><p>Reading from <code class="docutils literal notranslate"><span class="pre">HKLM\\Software</span></code> is allowed and results are merged with the <code class="file docutils literal notranslate"><span class="pre">registry.dat</span></code> file in the package.</p></li>
<li><p>Writing to <code class="docutils literal notranslate"><span class="pre">HKLM\\Software</span></code> is not allowed if the corresponding key/value exists, i.e. modifying existing keys.</p></li>
<li><p>Writing to <code class="docutils literal notranslate"><span class="pre">HKLM\\Software</span></code> is allowed as long as a corresponding key/value does not exist in the package
and the user has the correct access permissions.</p></li>
</ul>
<p>For more detail on the technical basis for these limitations, please consult
Microsoft’s documentation on packaged full-trust apps, currently available at
<a class="reference external" href="https://docs.microsoft.com/en-us/windows/msix/desktop/desktop-to-uwp-behind-the-scenes">docs.microsoft.com/en-us/windows/msix/desktop/desktop-to-uwp-behind-the-scenes</a></p>
</section>
</section>
</section>
<section id="the-nuget-org-packages">
<span id="windows-nuget"></span><h2><span class="section-number">4.3. </span>The nuget.org packages<a class="headerlink" href="#the-nuget-org-packages" title="Permalink to this headline">¶</a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.2.</span></p>
</div>
<p>The nuget.org package is a reduced size Python environment intended for use on
continuous integration and build systems that do not have a system-wide
install of Python. While nuget is “the package manager for .NET”, it also works
perfectly fine for packages containing build-time tools.</p>
<p>Visit <a class="reference external" href="https://www.nuget.org/">nuget.org</a> for the most up-to-date information
on using nuget. What follows is a summary that is sufficient for Python
developers.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">nuget.exe</span></code> command line tool may be downloaded directly from
<code class="docutils literal notranslate"><span class="pre">https://aka.ms/nugetclidl</span></code>, for example, using curl or PowerShell. With the
tool, the latest version of Python for 64-bit or 32-bit machines is installed
using:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>nuget.exe install python -ExcludeVersion -OutputDirectory .
nuget.exe install pythonx86 -ExcludeVersion -OutputDirectory .
</pre></div>
</div>
<p>To select a particular version, add a <code class="docutils literal notranslate"><span class="pre">-Version</span> <span class="pre">3.x.y</span></code>. The output directory
may be changed from <code class="docutils literal notranslate"><span class="pre">.</span></code>, and the package will be installed into a
subdirectory. By default, the subdirectory is named the same as the package,
and without the <code class="docutils literal notranslate"><span class="pre">-ExcludeVersion</span></code> option this name will include the specific
version installed. Inside the subdirectory is a <code class="docutils literal notranslate"><span class="pre">tools</span></code> directory that
contains the Python installation:</p>
<div class="highlight-doscon notranslate"><div class="highlight"><pre><span></span><span class="go"># Without -ExcludeVersion</span>
<span class="gp">&gt;</span> .\python.3.5.2\tools\python.exe -V
<span class="go">Python 3.5.2</span>

<span class="go"># With -ExcludeVersion</span>
<span class="gp">&gt;</span> .\python\tools\python.exe -V
<span class="go">Python 3.5.2</span>
</pre></div>
</div>
<p>In general, nuget packages are not upgradeable, and newer versions should be
installed side-by-side and referenced using the full path. Alternatively,
delete the package directory manually and install it again. Many CI systems
will do this automatically if they do not preserve files between builds.</p>
<p>Alongside the <code class="docutils literal notranslate"><span class="pre">tools</span></code> directory is a <code class="docutils literal notranslate"><span class="pre">build\native</span></code> directory. This
contains a MSBuild properties file <code class="docutils literal notranslate"><span class="pre">python.props</span></code> that can be used in a
C++ project to reference the Python install. Including the settings will
automatically use the headers and import libraries in your build.</p>
<p>The package information pages on nuget.org are
<a class="reference external" href="https://www.nuget.org/packages/python">www.nuget.org/packages/python</a>
for the 64-bit version and <a class="reference external" href="https://www.nuget.org/packages/pythonx86">www.nuget.org/packages/pythonx86</a> for the 32-bit version.</p>
</section>
<section id="the-embeddable-package">
<span id="windows-embeddable"></span><h2><span class="section-number">4.4. </span>The embeddable package<a class="headerlink" href="#the-embeddable-package" title="Permalink to this headline">¶</a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.</span></p>
</div>
<p>The embedded distribution is a ZIP file containing a minimal Python environment.
It is intended for acting as part of another application, rather than being
directly accessed by end-users.</p>
<p>When extracted, the embedded distribution is (almost) fully isolated from the
user’s system, including environment variables, system registry settings, and
installed packages. The standard library is included as pre-compiled and
optimized <code class="docutils literal notranslate"><span class="pre">.pyc</span></code> files in a ZIP, and <code class="docutils literal notranslate"><span class="pre">python3.dll</span></code>, <code class="docutils literal notranslate"><span class="pre">python37.dll</span></code>,
<code class="docutils literal notranslate"><span class="pre">python.exe</span></code> and <code class="docutils literal notranslate"><span class="pre">pythonw.exe</span></code> are all provided. Tcl/tk (including all
dependents, such as Idle), pip and the Python documentation are not included.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The embedded distribution does not include the <a class="reference external" href="https://docs.microsoft.com/en-US/cpp/windows/latest-supported-vc-redist#visual-studio-2015-2017-2019-and-2022">Microsoft C Runtime</a> and it is
the responsibility of the application installer to provide this. The
runtime may have already been installed on a user’s system previously or
automatically via Windows Update, and can be detected by finding
<code class="docutils literal notranslate"><span class="pre">ucrtbase.dll</span></code> in the system directory.</p>
</div>
<p>Third-party packages should be installed by the application installer alongside
the embedded distribution. Using pip to manage dependencies as for a regular
Python installation is not supported with this distribution, though with some
care it may be possible to include and use pip for automatic updates. In
general, third-party packages should be treated as part of the application
(“vendoring”) so that the developer can ensure compatibility with newer
versions before providing updates to users.</p>
<p>The two recommended use cases for this distribution are described below.</p>
<section id="python-application">
<h3><span class="section-number">4.4.1. </span>Python Application<a class="headerlink" href="#python-application" title="Permalink to this headline">¶</a></h3>
<p>An application written in Python does not necessarily require users to be aware
of that fact. The embedded distribution may be used in this case to include a
private version of Python in an install package. Depending on how transparent it
should be (or conversely, how professional it should appear), there are two
options.</p>
<p>Using a specialized executable as a launcher requires some coding, but provides
the most transparent experience for users. With a customized launcher, there are
no obvious indications that the program is running on Python: icons can be
customized, company and version information can be specified, and file
associations behave properly. In most cases, a custom launcher should simply be
able to call <code class="docutils literal notranslate"><span class="pre">Py_Main</span></code> with a hard-coded command line.</p>
<p>The simpler approach is to provide a batch file or generated shortcut that
directly calls the <code class="docutils literal notranslate"><span class="pre">python.exe</span></code> or <code class="docutils literal notranslate"><span class="pre">pythonw.exe</span></code> with the required
command-line arguments. In this case, the application will appear to be Python
and not its actual name, and users may have trouble distinguishing it from other
running Python processes or file associations.</p>
<p>With the latter approach, packages should be installed as directories alongside
the Python executable to ensure they are available on the path. With the
specialized launcher, packages can be located in other locations as there is an
opportunity to specify the search path before launching the application.</p>
</section>
<section id="embedding-python">
<h3><span class="section-number">4.4.2. </span>Embedding Python<a class="headerlink" href="#embedding-python" title="Permalink to this headline">¶</a></h3>
<p>Applications written in native code often require some form of scripting
language, and the embedded Python distribution can be used for this purpose. In
general, the majority of the application is in native code, and some part will
either invoke <code class="docutils literal notranslate"><span class="pre">python.exe</span></code> or directly use <code class="docutils literal notranslate"><span class="pre">python3.dll</span></code>. For either case,
extracting the embedded distribution to a subdirectory of the application
installation is sufficient to provide a loadable Python interpreter.</p>
<p>As with the application use, packages can be installed to any location as there
is an opportunity to specify search paths before initializing the interpreter.
Otherwise, there is no fundamental differences between using the embedded
distribution and a regular installation.</p>
</section>
</section>
<section id="alternative-bundles">
<h2><span class="section-number">4.5. </span>Alternative bundles<a class="headerlink" href="#alternative-bundles" title="Permalink to this headline">¶</a></h2>
<p>Besides the standard CPython distribution, there are modified packages including
additional functionality.  The following is a list of popular versions and their
key features:</p>
<dl>
<dt><a class="reference external" href="https://www.activestate.com/products/python/">ActivePython</a></dt><dd><p>Installer with multi-platform compatibility, documentation, PyWin32</p>
</dd>
<dt><a class="reference external" href="https://www.anaconda.com/download/">Anaconda</a></dt><dd><p>Popular scientific modules (such as numpy, scipy and pandas) and the
<code class="docutils literal notranslate"><span class="pre">conda</span></code> package manager.</p>
</dd>
<dt><a class="reference external" href="https://www.enthought.com/edm/">Enthought Deployment Manager</a></dt><dd><p>“The Next Generation Python Environment and Package Manager”.</p>
<p>Previously Enthought provided Canopy, but it <a class="reference external" href="https://support.enthought.com/hc/en-us/articles/360038600051-Canopy-GUI-end-of-life-transition-to-the-Enthought-Deployment-Manager-EDM-and-Visual-Studio-Code">reached end of life in 2016</a>.</p>
</dd>
<dt><a class="reference external" href="https://winpython.github.io/">WinPython</a></dt><dd><p>Windows-specific distribution with prebuilt scientific packages and
tools for building packages.</p>
</dd>
</dl>
<p>Note that these packages may not include the latest versions of Python or
other libraries, and are not maintained or supported by the core Python team.</p>
</section>
<section id="configuring-python">
<h2><span class="section-number">4.6. </span>Configuring Python<a class="headerlink" href="#configuring-python" title="Permalink to this headline">¶</a></h2>
<p>To run Python conveniently from a command prompt, you might consider changing
some default environment variables in Windows.  While the installer provides an
option to configure the PATH and PATHEXT variables for you, this is only
reliable for a single, system-wide installation.  If you regularly use multiple
versions of Python, consider using the <a class="reference internal" href="#launcher"><span class="std std-ref">Python Launcher for Windows</span></a>.</p>
<section id="excursus-setting-environment-variables">
<span id="setting-envvars"></span><h3><span class="section-number">4.6.1. </span>Excursus: Setting environment variables<a class="headerlink" href="#excursus-setting-environment-variables" title="Permalink to this headline">¶</a></h3>
<p>Windows allows environment variables to be configured permanently at both the
User level and the System level, or temporarily in a command prompt.</p>
<p>To temporarily set environment variables, open Command Prompt and use the
<strong class="command">set</strong> command:</p>
<div class="highlight-doscon notranslate"><div class="highlight"><pre><span></span><span class="gp">C:\&gt;</span><span class="k">set</span> <span class="nv">PATH</span><span class="p">=</span>C:\Program Files\Python 3.9;<span class="nv">%PATH%</span>
<span class="gp">C:\&gt;</span><span class="k">set</span> <span class="nv">PYTHONPATH</span><span class="p">=</span><span class="nv">%PYTHONPATH%</span>;C:\My_python_lib
<span class="gp">C:\&gt;</span>python
</pre></div>
</div>
<p>These changes will apply to any further commands executed in that console, and
will be inherited by any applications started from the console.</p>
<p>Including the variable name within percent signs will expand to the existing
value, allowing you to add your new value at either the start or the end.
Modifying <span class="target" id="index-9"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code> by adding the directory containing
<strong class="program">python.exe</strong> to the start is a common way to ensure the correct version
of Python is launched.</p>
<p>To permanently modify the default environment variables, click Start and search
for ‘edit environment variables’, or open System properties, <span class="guilabel">Advanced
system settings</span> and click the <span class="guilabel">Environment Variables</span> button.
In this dialog, you can add or modify User and System variables. To change
System variables, you need non-restricted access to your machine
(i.e. Administrator rights).</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Windows will concatenate User variables <em>after</em> System variables, which may
cause unexpected results when modifying <span class="target" id="index-10"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code>.</p>
<p>The <span class="target" id="index-11"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONPATH</span></code></a> variable is used by all versions of Python,
so you should not permanently configure it unless the listed paths
only include code that is compatible with all of your installed Python
versions.</p>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt><a class="reference external" href="https://docs.microsoft.com/en-us/windows/win32/procthread/environment-variables">https://docs.microsoft.com/en-us/windows/win32/procthread/environment-variables</a></dt><dd><p>Overview of environment variables on Windows</p>
</dd>
<dt><a class="reference external" href="https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/set_1">https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/set_1</a></dt><dd><p>The <code class="docutils literal notranslate"><span class="pre">set</span></code> command, for temporarily modifying environment variables</p>
</dd>
<dt><a class="reference external" href="https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/setx">https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/setx</a></dt><dd><p>The <code class="docutils literal notranslate"><span class="pre">setx</span></code> command, for permanently modifying environment variables</p>
</dd>
</dl>
</div>
</section>
<section id="finding-the-python-executable">
<span id="windows-path-mod"></span><h3><span class="section-number">4.6.2. </span>Finding the Python executable<a class="headerlink" href="#finding-the-python-executable" title="Permalink to this headline">¶</a></h3>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5.</span></p>
</div>
<p>Besides using the automatically created start menu entry for the Python
interpreter, you might want to start Python in the command prompt. The
installer has an option to set that up for you.</p>
<p>On the first page of the installer, an option labelled “Add Python to PATH”
may be selected to have the installer add the install location into the
<span class="target" id="index-12"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code>.  The location of the <code class="file docutils literal notranslate"><span class="pre">Scripts\</span></code> folder is also added.
This allows you to type <strong class="command">python</strong> to run the interpreter, and
<strong class="command">pip</strong> for the package installer. Thus, you can also execute your
scripts with command line options, see <a class="reference internal" href="cmdline.html#using-on-cmdline"><span class="std std-ref">Command line</span></a> documentation.</p>
<p>If you don’t enable this option at install time, you can always re-run the
installer, select Modify, and enable it.  Alternatively, you can manually
modify the <span class="target" id="index-13"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code> using the directions in <a class="reference internal" href="#setting-envvars"><span class="std std-ref">Excursus: Setting environment variables</span></a>.  You
need to set your <span class="target" id="index-14"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code> environment variable to include the directory
of your Python installation, delimited by a semicolon from other entries.  An
example variable could look like this (assuming the first two entries already
existed):</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>C:\WINDOWS\system32;C:\WINDOWS;C:\Program Files\Python 3.9
</pre></div>
</div>
</section>
</section>
<section id="utf-8-mode">
<span id="win-utf8-mode"></span><h2><span class="section-number">4.7. </span>UTF-8 mode<a class="headerlink" href="#utf-8-mode" title="Permalink to this headline">¶</a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
<p>Windows still uses legacy encodings for the system encoding (the ANSI Code
Page).  Python uses it for the default encoding of text files (e.g.
<a class="reference internal" href="../library/locale.html#locale.getencoding" title="locale.getencoding"><code class="xref py py-func docutils literal notranslate"><span class="pre">locale.getencoding()</span></code></a>).</p>
<p>This may cause issues because UTF-8 is widely used on the internet
and most Unix systems, including WSL (Windows Subsystem for Linux).</p>
<p>You can use the <a class="reference internal" href="../library/os.html#utf8-mode"><span class="std std-ref">Python UTF-8 Mode</span></a> to change the default text
encoding to UTF-8. You can enable the <a class="reference internal" href="../library/os.html#utf8-mode"><span class="std std-ref">Python UTF-8 Mode</span></a> via
the <code class="docutils literal notranslate"><span class="pre">-X</span> <span class="pre">utf8</span></code> command line option, or the <code class="docutils literal notranslate"><span class="pre">PYTHONUTF8=1</span></code> environment
variable.  See <span class="target" id="index-15"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONUTF8"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONUTF8</span></code></a> for enabling UTF-8 mode, and
<a class="reference internal" href="#setting-envvars"><span class="std std-ref">Excursus: Setting environment variables</span></a> for how to modify environment variables.</p>
<p>When the <a class="reference internal" href="../library/os.html#utf8-mode"><span class="std std-ref">Python UTF-8 Mode</span></a> is enabled, you can still use the
system encoding (the ANSI Code Page) via the “mbcs” codec.</p>
<p>Note that adding <code class="docutils literal notranslate"><span class="pre">PYTHONUTF8=1</span></code> to the default environment variables
will affect all Python 3.7+ applications on your system.
If you have any Python 3.7+ applications which rely on the legacy
system encoding, it is recommended to set the environment variable
temporarily or use the <code class="docutils literal notranslate"><span class="pre">-X</span> <span class="pre">utf8</span></code> command line option.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Even when UTF-8 mode is disabled, Python uses UTF-8 by default
on Windows for:</p>
<ul class="simple">
<li><p>Console I/O including standard I/O (see <span class="target" id="index-16"></span><a class="pep reference external" href="https://peps.python.org/pep-0528/"><strong>PEP 528</strong></a> for details).</p></li>
<li><p>The <a class="reference internal" href="../glossary.html#term-filesystem-encoding-and-error-handler"><span class="xref std std-term">filesystem encoding</span></a>
(see <span class="target" id="index-17"></span><a class="pep reference external" href="https://peps.python.org/pep-0529/"><strong>PEP 529</strong></a> for details).</p></li>
</ul>
</div>
</section>
<section id="python-launcher-for-windows">
<span id="launcher"></span><h2><span class="section-number">4.8. </span>Python Launcher for Windows<a class="headerlink" href="#python-launcher-for-windows" title="Permalink to this headline">¶</a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.3.</span></p>
</div>
<p>The Python launcher for Windows is a utility which aids in locating and
executing of different Python versions.  It allows scripts (or the
command-line) to indicate a preference for a specific Python version, and
will locate and execute that version.</p>
<p>Unlike the <span class="target" id="index-18"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code> variable, the launcher will correctly select the most
appropriate version of Python. It will prefer per-user installations over
system-wide ones, and orders by language version rather than using the most
recently installed version.</p>
<p>The launcher was originally specified in <span class="target" id="index-19"></span><a class="pep reference external" href="https://peps.python.org/pep-0397/"><strong>PEP 397</strong></a>.</p>
<section id="getting-started">
<h3><span class="section-number">4.8.1. </span>Getting started<a class="headerlink" href="#getting-started" title="Permalink to this headline">¶</a></h3>
<section id="from-the-command-line">
<h4><span class="section-number">4.8.1.1. </span>From the command-line<a class="headerlink" href="#from-the-command-line" title="Permalink to this headline">¶</a></h4>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.6.</span></p>
</div>
<p>System-wide installations of Python 3.3 and later will put the launcher on your
<span class="target" id="index-20"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code>. The launcher is compatible with all available versions of
Python, so it does not matter which version is installed. To check that the
launcher is available, execute the following command in Command Prompt:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>py
</pre></div>
</div>
<p>You should find that the latest version of Python you have installed is
started - it can be exited as normal, and any additional command-line
arguments specified will be sent directly to Python.</p>
<p>If you have multiple versions of Python installed (e.g., 3.7 and 3.12) you
will have noticed that Python 3.12 was started - to launch Python 3.7, try
the command:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>py -3.7
</pre></div>
</div>
<p>If you want the latest version of Python 2 you have installed, try the
command:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>py -2
</pre></div>
</div>
<p>If you see the following error, you do not have the launcher installed:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&#39;py&#39; is not recognized as an internal or external command,
operable program or batch file.
</pre></div>
</div>
<p>The command:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>py --list
</pre></div>
</div>
<p>displays the currently installed version(s) of Python.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">-x.y</span></code> argument is the short form of the <code class="docutils literal notranslate"><span class="pre">-V:Company/Tag</span></code> argument,
which allows selecting a specific Python runtime, including those that may have
come from somewhere other than python.org. Any runtime registered by following
<span class="target" id="index-21"></span><a class="pep reference external" href="https://peps.python.org/pep-0514/"><strong>PEP 514</strong></a> will be discoverable. The <code class="docutils literal notranslate"><span class="pre">--list</span></code> command lists all available
runtimes using the <code class="docutils literal notranslate"><span class="pre">-V:</span></code> format.</p>
<p>When using the <code class="docutils literal notranslate"><span class="pre">-V:</span></code> argument, specifying the Company will limit selection to
runtimes from that provider, while specifying only the Tag will select from all
providers. Note that omitting the slash implies a tag:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span># Select any &#39;3.*&#39; tagged runtime
py -V:3

# Select any &#39;PythonCore&#39; released runtime
py -V:PythonCore/

# Select PythonCore&#39;s latest Python 3 runtime
py -V:PythonCore/3
</pre></div>
</div>
<p>The short form of the argument (<code class="docutils literal notranslate"><span class="pre">-3</span></code>) only ever selects from core Python
releases, and not other distributions. However, the longer form (<code class="docutils literal notranslate"><span class="pre">-V:3</span></code>) will
select from any.</p>
<p>The Company is matched on the full string, case-insenitive. The Tag is matched
oneither the full string, or a prefix, provided the next character is a dot or a
hyphen. This allows <code class="docutils literal notranslate"><span class="pre">-V:3.1</span></code> to match <code class="docutils literal notranslate"><span class="pre">3.1-32</span></code>, but not <code class="docutils literal notranslate"><span class="pre">3.10</span></code>. Tags are
sorted using numerical ordering (<code class="docutils literal notranslate"><span class="pre">3.10</span></code> is newer than <code class="docutils literal notranslate"><span class="pre">3.1</span></code>), but are
compared using text (<code class="docutils literal notranslate"><span class="pre">-V:3.01</span></code> does not match <code class="docutils literal notranslate"><span class="pre">3.1</span></code>).</p>
</section>
<section id="virtual-environments">
<h4><span class="section-number">4.8.1.2. </span>Virtual environments<a class="headerlink" href="#virtual-environments" title="Permalink to this headline">¶</a></h4>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.</span></p>
</div>
<p>If the launcher is run with no explicit Python version specification, and a
virtual environment (created with the standard library <a class="reference internal" href="../library/venv.html#module-venv" title="venv: Creation of virtual environments."><code class="xref py py-mod docutils literal notranslate"><span class="pre">venv</span></code></a> module or
the external <code class="docutils literal notranslate"><span class="pre">virtualenv</span></code> tool) active, the launcher will run the virtual
environment’s interpreter rather than the global one.  To run the global
interpreter, either deactivate the virtual environment, or explicitly specify
the global Python version.</p>
</section>
<section id="from-a-script">
<h4><span class="section-number">4.8.1.3. </span>From a script<a class="headerlink" href="#from-a-script" title="Permalink to this headline">¶</a></h4>
<p>Let’s create a test Python script - create a file called <code class="docutils literal notranslate"><span class="pre">hello.py</span></code> with the
following contents</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="ch">#! python</span>
<span class="kn">import</span> <span class="nn">sys</span>
<span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">&quot;hello from Python </span><span class="si">%s</span><span class="se">\n</span><span class="s2">&quot;</span> <span class="o">%</span> <span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">version</span><span class="p">,))</span>
</pre></div>
</div>
<p>From the directory in which hello.py lives, execute the command:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>py hello.py
</pre></div>
</div>
<p>You should notice the version number of your latest Python 2.x installation
is printed.  Now try changing the first line to be:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="ch">#! python3</span>
</pre></div>
</div>
<p>Re-executing the command should now print the latest Python 3.x information.
As with the above command-line examples, you can specify a more explicit
version qualifier.  Assuming you have Python 3.7 installed, try changing
the first line to <code class="docutils literal notranslate"><span class="pre">#!</span> <span class="pre">python3.7</span></code> and you should find the 3.7
version information printed.</p>
<p>Note that unlike interactive use, a bare “python” will use the latest
version of Python 2.x that you have installed.  This is for backward
compatibility and for compatibility with Unix, where the command <code class="docutils literal notranslate"><span class="pre">python</span></code>
typically refers to Python 2.</p>
</section>
<section id="from-file-associations">
<h4><span class="section-number">4.8.1.4. </span>From file associations<a class="headerlink" href="#from-file-associations" title="Permalink to this headline">¶</a></h4>
<p>The launcher should have been associated with Python files (i.e. <code class="docutils literal notranslate"><span class="pre">.py</span></code>,
<code class="docutils literal notranslate"><span class="pre">.pyw</span></code>, <code class="docutils literal notranslate"><span class="pre">.pyc</span></code> files) when it was installed.  This means that
when you double-click on one of these files from Windows explorer the launcher
will be used, and therefore you can use the same facilities described above to
have the script specify the version which should be used.</p>
<p>The key benefit of this is that a single launcher can support multiple Python
versions at the same time depending on the contents of the first line.</p>
</section>
</section>
<section id="shebang-lines">
<h3><span class="section-number">4.8.2. </span>Shebang Lines<a class="headerlink" href="#shebang-lines" title="Permalink to this headline">¶</a></h3>
<p>If the first line of a script file starts with <code class="docutils literal notranslate"><span class="pre">#!</span></code>, it is known as a
“shebang” line.  Linux and other Unix like operating systems have native
support for such lines and they are commonly used on such systems to indicate
how a script should be executed.  This launcher allows the same facilities to
be used with Python scripts on Windows and the examples above demonstrate their
use.</p>
<p>To allow shebang lines in Python scripts to be portable between Unix and
Windows, this launcher supports a number of ‘virtual’ commands to specify
which interpreter to use.  The supported virtual commands are:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">/usr/bin/env</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">/usr/bin/python</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">/usr/local/bin/python</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">python</span></code></p></li>
</ul>
<p>For example, if the first line of your script starts with</p>
<div class="highlight-sh notranslate"><div class="highlight"><pre><span></span><span class="ch">#! /usr/bin/python</span>
</pre></div>
</div>
<p>The default Python will be located and used.  As many Python scripts written
to work on Unix will already have this line, you should find these scripts can
be used by the launcher without modification.  If you are writing a new script
on Windows which you hope will be useful on Unix, you should use one of the
shebang lines starting with <code class="docutils literal notranslate"><span class="pre">/usr</span></code>.</p>
<p>Any of the above virtual commands can be suffixed with an explicit version
(either just the major version, or the major and minor version).
Furthermore the 32-bit version can be requested by adding “-32” after the
minor version. I.e. <code class="docutils literal notranslate"><span class="pre">/usr/bin/python3.7-32</span></code> will request usage of the
32-bit python 3.7.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7: </span>Beginning with python launcher 3.7 it is possible to request 64-bit version
by the “-64” suffix. Furthermore it is possible to specify a major and
architecture without minor (i.e. <code class="docutils literal notranslate"><span class="pre">/usr/bin/python3-64</span></code>).</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.11: </span>The “-64” suffix is deprecated, and now implies “any architecture that is
not provably i386/32-bit”. To request a specific environment, use the new
<code class="samp docutils literal notranslate"><span class="pre">-V:</span><em><span class="pre">TAG</span></em></code> argument with the complete tag.</p>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">/usr/bin/env</span></code> form of shebang line has one further special property.
Before looking for installed Python interpreters, this form will search the
executable <span class="target" id="index-22"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code> for a Python executable matching the name provided
as the first argument. This corresponds to the behaviour of the Unix <code class="docutils literal notranslate"><span class="pre">env</span></code>
program, which performs a <span class="target" id="index-23"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code> search.
If an executable matching the first argument after the <code class="docutils literal notranslate"><span class="pre">env</span></code> command cannot
be found, but the argument starts with <code class="docutils literal notranslate"><span class="pre">python</span></code>, it will be handled as
described for the other virtual commands.
The environment variable <span class="target" id="index-24"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYLAUNCHER_NO_SEARCH_PATH</span></code> may be set
(to any value) to skip this search of <span class="target" id="index-25"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code>.</p>
<p>Shebang lines that do not match any of these patterns are looked up in the
<code class="docutils literal notranslate"><span class="pre">[commands]</span></code> section of the launcher’s <a class="reference internal" href="#launcher-ini"><span class="std std-ref">.INI file</span></a>.
This may be used to handle certain commands in a way that makes sense for your
system. The name of the command must be a single argument (no spaces in the
shebang executable), and the value substituted is the full path to the
executable (additional arguments specified in the .INI will be quoted as part
of the filename).</p>
<div class="highlight-ini notranslate"><div class="highlight"><pre><span></span><span class="k">[commands]</span>
<span class="na">/bin/xpython</span><span class="o">=</span><span class="s">C:\Program Files\XPython\python.exe</span>
</pre></div>
</div>
<p>Any commands not found in the .INI file are treated as <strong>Windows</strong> executable
paths that are absolute or relative to the directory containing the script file.
This is a convenience for Windows-only scripts, such as those generated by an
installer, since the behavior is not compatible with Unix-style shells.
These paths may be quoted, and may include multiple arguments, after which the
path to the script and any additional arguments will be appended.</p>
</section>
<section id="arguments-in-shebang-lines">
<h3><span class="section-number">4.8.3. </span>Arguments in shebang lines<a class="headerlink" href="#arguments-in-shebang-lines" title="Permalink to this headline">¶</a></h3>
<p>The shebang lines can also specify additional options to be passed to the
Python interpreter.  For example, if you have a shebang line:</p>
<div class="highlight-sh notranslate"><div class="highlight"><pre><span></span><span class="ch">#! /usr/bin/python -v</span>
</pre></div>
</div>
<p>Then Python will be started with the <code class="docutils literal notranslate"><span class="pre">-v</span></code> option</p>
</section>
<section id="customization">
<h3><span class="section-number">4.8.4. </span>Customization<a class="headerlink" href="#customization" title="Permalink to this headline">¶</a></h3>
<section id="customization-via-ini-files">
<span id="launcher-ini"></span><h4><span class="section-number">4.8.4.1. </span>Customization via INI files<a class="headerlink" href="#customization-via-ini-files" title="Permalink to this headline">¶</a></h4>
<p>Two .ini files will be searched by the launcher - <code class="docutils literal notranslate"><span class="pre">py.ini</span></code> in the current
user’s application data directory (<code class="docutils literal notranslate"><span class="pre">%LOCALAPPDATA%</span></code> or <code class="docutils literal notranslate"><span class="pre">$env:LocalAppData</span></code>)
and <code class="docutils literal notranslate"><span class="pre">py.ini</span></code> in the same directory as the launcher. The same .ini files are
used for both the ‘console’ version of the launcher (i.e. py.exe) and for the
‘windows’ version (i.e. pyw.exe).</p>
<p>Customization specified in the “application directory” will have precedence over
the one next to the executable, so a user, who may not have write access to the
.ini file next to the launcher, can override commands in that global .ini file.</p>
</section>
<section id="customizing-default-python-versions">
<h4><span class="section-number">4.8.4.2. </span>Customizing default Python versions<a class="headerlink" href="#customizing-default-python-versions" title="Permalink to this headline">¶</a></h4>
<p>In some cases, a version qualifier can be included in a command to dictate
which version of Python will be used by the command. A version qualifier
starts with a major version number and can optionally be followed by a period
(‘.’) and a minor version specifier. Furthermore it is possible to specify
if a 32 or 64 bit implementation shall be requested by adding “-32” or “-64”.</p>
<p>For example, a shebang line of <code class="docutils literal notranslate"><span class="pre">#!python</span></code> has no version qualifier, while
<code class="docutils literal notranslate"><span class="pre">#!python3</span></code> has a version qualifier which specifies only a major version.</p>
<p>If no version qualifiers are found in a command, the environment
variable <span class="target" id="index-26"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PY_PYTHON</span></code> can be set to specify the default version
qualifier. If it is not set, the default is “3”. The variable can
specify any value that may be passed on the command line, such as “3”,
“3.7”, “3.7-32” or “3.7-64”. (Note that the “-64” option is only
available with the launcher included with Python 3.7 or newer.)</p>
<p>If no minor version qualifiers are found, the environment variable
<code class="docutils literal notranslate"><span class="pre">PY_PYTHON{major}</span></code> (where <code class="docutils literal notranslate"><span class="pre">{major}</span></code> is the current major version qualifier
as determined above) can be set to specify the full version. If no such option
is found, the launcher will enumerate the installed Python versions and use
the latest minor release found for the major version, which is likely,
although not guaranteed, to be the most recently installed version in that
family.</p>
<p>On 64-bit Windows with both 32-bit and 64-bit implementations of the same
(major.minor) Python version installed, the 64-bit version will always be
preferred. This will be true for both 32-bit and 64-bit implementations of the
launcher - a 32-bit launcher will prefer to execute a 64-bit Python installation
of the specified version if available. This is so the behavior of the launcher
can be predicted knowing only what versions are installed on the PC and
without regard to the order in which they were installed (i.e., without knowing
whether a 32 or 64-bit version of Python and corresponding launcher was
installed last). As noted above, an optional “-32” or “-64” suffix can be
used on a version specifier to change this behaviour.</p>
<p>Examples:</p>
<ul class="simple">
<li><p>If no relevant options are set, the commands <code class="docutils literal notranslate"><span class="pre">python</span></code> and
<code class="docutils literal notranslate"><span class="pre">python2</span></code> will use the latest Python 2.x version installed and
the command <code class="docutils literal notranslate"><span class="pre">python3</span></code> will use the latest Python 3.x installed.</p></li>
<li><p>The command <code class="docutils literal notranslate"><span class="pre">python3.7</span></code> will not consult any
options at all as the versions are fully specified.</p></li>
<li><p>If <code class="docutils literal notranslate"><span class="pre">PY_PYTHON=3</span></code>, the commands <code class="docutils literal notranslate"><span class="pre">python</span></code> and <code class="docutils literal notranslate"><span class="pre">python3</span></code> will both use
the latest installed Python 3 version.</p></li>
<li><p>If <code class="docutils literal notranslate"><span class="pre">PY_PYTHON=3.7-32</span></code>, the command <code class="docutils literal notranslate"><span class="pre">python</span></code> will use the 32-bit
implementation of 3.7 whereas the command <code class="docutils literal notranslate"><span class="pre">python3</span></code> will use the latest
installed Python (PY_PYTHON was not considered at all as a major
version was specified.)</p></li>
<li><p>If <code class="docutils literal notranslate"><span class="pre">PY_PYTHON=3</span></code> and <code class="docutils literal notranslate"><span class="pre">PY_PYTHON3=3.7</span></code>, the commands
<code class="docutils literal notranslate"><span class="pre">python</span></code> and <code class="docutils literal notranslate"><span class="pre">python3</span></code> will both use specifically 3.7</p></li>
</ul>
<p>In addition to environment variables, the same settings can be configured
in the .INI file used by the launcher.  The section in the INI file is
called <code class="docutils literal notranslate"><span class="pre">[defaults]</span></code> and the key name will be the same as the
environment variables without the leading <code class="docutils literal notranslate"><span class="pre">PY_</span></code> prefix (and note that
the key names in the INI file are case insensitive.)  The contents of
an environment variable will override things specified in the INI file.</p>
<p>For example:</p>
<ul class="simple">
<li><p>Setting <code class="docutils literal notranslate"><span class="pre">PY_PYTHON=3.7</span></code> is equivalent to the INI file containing:</p></li>
</ul>
<div class="highlight-ini notranslate"><div class="highlight"><pre><span></span><span class="k">[defaults]</span>
<span class="na">python</span><span class="o">=</span><span class="s">3.7</span>
</pre></div>
</div>
<ul class="simple">
<li><p>Setting <code class="docutils literal notranslate"><span class="pre">PY_PYTHON=3</span></code> and <code class="docutils literal notranslate"><span class="pre">PY_PYTHON3=3.7</span></code> is equivalent to the INI file
containing:</p></li>
</ul>
<div class="highlight-ini notranslate"><div class="highlight"><pre><span></span><span class="k">[defaults]</span>
<span class="na">python</span><span class="o">=</span><span class="s">3</span>
<span class="na">python3</span><span class="o">=</span><span class="s">3.7</span>
</pre></div>
</div>
</section>
</section>
<section id="diagnostics">
<h3><span class="section-number">4.8.5. </span>Diagnostics<a class="headerlink" href="#diagnostics" title="Permalink to this headline">¶</a></h3>
<p>If an environment variable <span class="target" id="index-27"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYLAUNCHER_DEBUG</span></code> is set (to any value), the
launcher will print diagnostic information to stderr (i.e. to the console).
While this information manages to be simultaneously verbose <em>and</em> terse, it
should allow you to see what versions of Python were located, why a
particular version was chosen and the exact command-line used to execute the
target Python. It is primarily intended for testing and debugging.</p>
</section>
<section id="dry-run">
<h3><span class="section-number">4.8.6. </span>Dry Run<a class="headerlink" href="#dry-run" title="Permalink to this headline">¶</a></h3>
<p>If an environment variable <span class="target" id="index-28"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYLAUNCHER_DRYRUN</span></code> is set (to any value),
the launcher will output the command it would have run, but will not actually
launch Python. This may be useful for tools that want to use the launcher to
detect and then launch Python directly. Note that the command written to
standard output is always encoded using UTF-8, and may not render correctly in
the console.</p>
</section>
<section id="install-on-demand">
<h3><span class="section-number">4.8.7. </span>Install on demand<a class="headerlink" href="#install-on-demand" title="Permalink to this headline">¶</a></h3>
<p>If an environment variable <span class="target" id="index-29"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYLAUNCHER_ALLOW_INSTALL</span></code> is set (to any
value), and the requested Python version is not installed but is available on
the Microsoft Store, the launcher will attempt to install it. This may require
user interaction to complete, and you may need to run the command again.</p>
<p>An additional <span class="target" id="index-30"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYLAUNCHER_ALWAYS_INSTALL</span></code> variable causes the launcher
to always try to install Python, even if it is detected. This is mainly intended
for testing (and should be used with <span class="target" id="index-31"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYLAUNCHER_DRYRUN</span></code>).</p>
</section>
<section id="return-codes">
<h3><span class="section-number">4.8.8. </span>Return codes<a class="headerlink" href="#return-codes" title="Permalink to this headline">¶</a></h3>
<p>The following exit codes may be returned by the Python launcher. Unfortunately,
there is no way to distinguish these from the exit code of Python itself.</p>
<p>The names of codes are as used in the sources, and are only for reference. There
is no way to access or resolve them apart from reading this page. Entries are
listed in alphabetical order of names.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 26%" />
<col style="width: 10%" />
<col style="width: 64%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Name</p></th>
<th class="head"><p>Value</p></th>
<th class="head"><p>Description</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>RC_BAD_VENV_CFG</p></td>
<td><p>107</p></td>
<td><p>A <code class="file docutils literal notranslate"><span class="pre">pyvenv.cfg</span></code> was found but is corrupt.</p></td>
</tr>
<tr class="row-odd"><td><p>RC_CREATE_PROCESS</p></td>
<td><p>101</p></td>
<td><p>Failed to launch Python.</p></td>
</tr>
<tr class="row-even"><td><p>RC_INSTALLING</p></td>
<td><p>111</p></td>
<td><p>An install was started, but the command will
need to be re-run after it completes.</p></td>
</tr>
<tr class="row-odd"><td><p>RC_INTERNAL_ERROR</p></td>
<td><p>109</p></td>
<td><p>Unexpected error. Please report a bug.</p></td>
</tr>
<tr class="row-even"><td><p>RC_NO_COMMANDLINE</p></td>
<td><p>108</p></td>
<td><p>Unable to obtain command line from the
operating system.</p></td>
</tr>
<tr class="row-odd"><td><p>RC_NO_PYTHON</p></td>
<td><p>103</p></td>
<td><p>Unable to locate the requested version.</p></td>
</tr>
<tr class="row-even"><td><p>RC_NO_VENV_CFG</p></td>
<td><p>106</p></td>
<td><p>A <code class="file docutils literal notranslate"><span class="pre">pyvenv.cfg</span></code> was required but not
found.</p></td>
</tr>
</tbody>
</table>
</section>
</section>
<section id="finding-modules">
<span id="windows-finding-modules"></span><h2><span class="section-number">4.9. </span>Finding modules<a class="headerlink" href="#finding-modules" title="Permalink to this headline">¶</a></h2>
<p>These notes supplement the description at <a class="reference internal" href="../library/sys_path_init.html#sys-path-init"><span class="std std-ref">The initialization of the sys.path module search path</span></a> with
detailed Windows notes.</p>
<p>When no <code class="docutils literal notranslate"><span class="pre">._pth</span></code> file is found, this is how <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.path</span></code></a> is populated on
Windows:</p>
<ul class="simple">
<li><p>An empty entry is added at the start, which corresponds to the current
directory.</p></li>
<li><p>If the environment variable <span class="target" id="index-32"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONPATH</span></code></a> exists, as described in
<a class="reference internal" href="cmdline.html#using-on-envvars"><span class="std std-ref">Environment variables</span></a>, its entries are added next.  Note that on Windows,
paths in this variable must be separated by semicolons, to distinguish them
from the colon used in drive identifiers (<code class="docutils literal notranslate"><span class="pre">C:\</span></code> etc.).</p></li>
<li><p>Additional “application paths” can be added in the registry as subkeys of
<code class="samp docutils literal notranslate"><span class="pre">\SOFTWARE\Python\PythonCore{version}\PythonPath</span></code> under both the
<code class="docutils literal notranslate"><span class="pre">HKEY_CURRENT_USER</span></code> and <code class="docutils literal notranslate"><span class="pre">HKEY_LOCAL_MACHINE</span></code> hives.  Subkeys which have
semicolon-delimited path strings as their default value will cause each path
to be added to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.path</span></code></a>.  (Note that all known installers only use
HKLM, so HKCU is typically empty.)</p></li>
<li><p>If the environment variable <span class="target" id="index-33"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONHOME</span></code></a> is set, it is assumed as
“Python Home”.  Otherwise, the path of the main Python executable is used to
locate a “landmark file” (either <code class="docutils literal notranslate"><span class="pre">Lib\os.py</span></code> or <code class="docutils literal notranslate"><span class="pre">pythonXY.zip</span></code>) to deduce
the “Python Home”.  If a Python home is found, the relevant sub-directories
added to <a class="reference internal" href="../library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.path</span></code></a> (<code class="docutils literal notranslate"><span class="pre">Lib</span></code>, <code class="docutils literal notranslate"><span class="pre">plat-win</span></code>, etc) are based on that
folder.  Otherwise, the core Python path is constructed from the PythonPath
stored in the registry.</p></li>
<li><p>If the Python Home cannot be located, no <span class="target" id="index-34"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONPATH</span></code></a> is specified in
the environment, and no registry entries can be found, a default path with
relative entries is used (e.g. <code class="docutils literal notranslate"><span class="pre">.\Lib;.\plat-win</span></code>, etc).</p></li>
</ul>
<p>If a <code class="docutils literal notranslate"><span class="pre">pyvenv.cfg</span></code> file is found alongside the main executable or in the
directory one level above the executable, the following variations apply:</p>
<ul class="simple">
<li><p>If <code class="docutils literal notranslate"><span class="pre">home</span></code> is an absolute path and <span class="target" id="index-35"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONHOME</span></code></a> is not set, this
path is used instead of the path to the main executable when deducing the
home location.</p></li>
</ul>
<p>The end result of all this is:</p>
<ul class="simple">
<li><p>When running <code class="file docutils literal notranslate"><span class="pre">python.exe</span></code>, or any other .exe in the main Python
directory (either an installed version, or directly from the PCbuild
directory), the core path is deduced, and the core paths in the registry are
ignored.  Other “application paths” in the registry are always read.</p></li>
<li><p>When Python is hosted in another .exe (different directory, embedded via COM,
etc), the “Python Home” will not be deduced, so the core path from the
registry is used.  Other “application paths” in the registry are always read.</p></li>
<li><p>If Python can’t find its home and there are no registry value (frozen .exe,
some very strange installation setup) you get a path with some default, but
relative, paths.</p></li>
</ul>
<p>For those who want to bundle Python into their application or distribution, the
following advice will prevent conflicts with other installations:</p>
<ul class="simple">
<li><p>Include a <code class="docutils literal notranslate"><span class="pre">._pth</span></code> file alongside your executable containing the
directories to include. This will ignore paths listed in the registry and
environment variables, and also ignore <a class="reference internal" href="../library/site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal notranslate"><span class="pre">site</span></code></a> unless <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">site</span></code> is
listed.</p></li>
<li><p>If you are loading <code class="file docutils literal notranslate"><span class="pre">python3.dll</span></code> or <code class="file docutils literal notranslate"><span class="pre">python37.dll</span></code> in your own
executable, explicitly call <a class="reference internal" href="../c-api/init.html#c.Py_SetPath" title="Py_SetPath"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetPath()</span></code></a> or (at least)
<a class="reference internal" href="../c-api/init.html#c.Py_SetProgramName" title="Py_SetProgramName"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_SetProgramName()</span></code></a> before <a class="reference internal" href="../c-api/init.html#c.Py_Initialize" title="Py_Initialize"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_Initialize()</span></code></a>.</p></li>
<li><p>Clear and/or overwrite <span class="target" id="index-36"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONPATH</span></code></a> and set <span class="target" id="index-37"></span><a class="reference internal" href="cmdline.html#envvar-PYTHONHOME"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONHOME</span></code></a>
before launching <code class="file docutils literal notranslate"><span class="pre">python.exe</span></code> from your application.</p></li>
<li><p>If you cannot use the previous suggestions (for example, you are a
distribution that allows people to run <code class="file docutils literal notranslate"><span class="pre">python.exe</span></code> directly), ensure
that the landmark file (<code class="file docutils literal notranslate"><span class="pre">Lib\os.py</span></code>) exists in your install directory.
(Note that it will not be detected inside a ZIP file, but a correctly named
ZIP file will be detected instead.)</p></li>
</ul>
<p>These will ensure that the files in a system-wide installation will not take
precedence over the copy of the standard library bundled with your application.
Otherwise, your users may experience problems using your application. Note that
the first suggestion is the best, as the others may still be susceptible to
non-standard paths in the registry and user site-packages.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.6: </span></p>
<blockquote>
<div><ul class="simple">
<li><p>Adds <code class="docutils literal notranslate"><span class="pre">._pth</span></code> file support and removes <code class="docutils literal notranslate"><span class="pre">applocal</span></code> option from
<code class="docutils literal notranslate"><span class="pre">pyvenv.cfg</span></code>.</p></li>
<li><p>Adds <code class="file docutils literal notranslate"><span class="pre">python</span><em><span class="pre">XX</span></em><span class="pre">.zip</span></code> as a potential landmark when directly adjacent
to the executable.</p></li>
</ul>
</div></blockquote>
</div>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 3.6: </span></p>
<blockquote>
<div><p>Modules specified in the registry under <code class="docutils literal notranslate"><span class="pre">Modules</span></code> (not <code class="docutils literal notranslate"><span class="pre">PythonPath</span></code>)
may be imported by <a class="reference internal" href="../library/importlib.html#importlib.machinery.WindowsRegistryFinder" title="importlib.machinery.WindowsRegistryFinder"><code class="xref py py-class docutils literal notranslate"><span class="pre">importlib.machinery.WindowsRegistryFinder</span></code></a>.
This finder is enabled on Windows in 3.6.0 and earlier, but may need to
be explicitly added to <a class="reference internal" href="../library/sys.html#sys.meta_path" title="sys.meta_path"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.meta_path</span></code></a> in the future.</p>
</div></blockquote>
</div>
</section>
<section id="additional-modules">
<h2><span class="section-number">4.10. </span>Additional modules<a class="headerlink" href="#additional-modules" title="Permalink to this headline">¶</a></h2>
<p>Even though Python aims to be portable among all platforms, there are features
that are unique to Windows.  A couple of modules, both in the standard library
and external, and snippets exist to use these features.</p>
<p>The Windows-specific standard modules are documented in
<a class="reference internal" href="../library/windows.html#mswin-specific-services"><span class="std std-ref">MS Windows Specific Services</span></a>.</p>
<section id="pywin32">
<h3><span class="section-number">4.10.1. </span>PyWin32<a class="headerlink" href="#pywin32" title="Permalink to this headline">¶</a></h3>
<p>The <a class="reference external" href="https://pypi.org/project/pywin32">PyWin32</a> module by Mark Hammond
is a collection of modules for advanced Windows-specific support.  This includes
utilities for:</p>
<ul class="simple">
<li><p><a class="reference external" href="https://docs.microsoft.com/en-us/windows/win32/com/component-object-model--com--portal">Component Object Model</a>
(COM)</p></li>
<li><p>Win32 API calls</p></li>
<li><p>Registry</p></li>
<li><p>Event log</p></li>
<li><p><a class="reference external" href="https://docs.microsoft.com/en-us/cpp/mfc/mfc-desktop-applications">Microsoft Foundation Classes</a>
(MFC) user interfaces</p></li>
</ul>
<p><a class="reference external" href="https://web.archive.org/web/20060524042422/https://www.python.org/windows/pythonwin/">PythonWin</a> is a sample MFC application
shipped with PyWin32.  It is an embeddable IDE with a built-in debugger.</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt><a class="reference external" href="http://timgolden.me.uk/python/win32_how_do_i.html">Win32 How Do I…?</a></dt><dd><p>by Tim Golden</p>
</dd>
<dt><a class="reference external" href="https://www.boddie.org.uk/python/COM.html">Python and COM</a></dt><dd><p>by David and Paul Boddie</p>
</dd>
</dl>
</div>
</section>
<section id="cx-freeze">
<h3><span class="section-number">4.10.2. </span>cx_Freeze<a class="headerlink" href="#cx-freeze" title="Permalink to this headline">¶</a></h3>
<p><a class="reference external" href="https://cx-freeze.readthedocs.io/en/latest/">cx_Freeze</a>
wraps Python scripts into executable Windows programs
(<code class="file docutils literal notranslate"><em><span class="pre">*</span></em><span class="pre">.exe</span></code> files).  When you have done this, you can distribute your
application without requiring your users to install Python.</p>
</section>
</section>
<section id="compiling-python-on-windows">
<h2><span class="section-number">4.11. </span>Compiling Python on Windows<a class="headerlink" href="#compiling-python-on-windows" title="Permalink to this headline">¶</a></h2>
<p>If you want to compile CPython yourself, first thing you should do is get the
<a class="reference external" href="https://www.python.org/downloads/source/">source</a>. You can download either the
latest release’s source or just grab a fresh <a class="reference external" href="https://devguide.python.org/setup/#get-the-source-code">checkout</a>.</p>
<p>The source tree contains a build solution and project files for Microsoft
Visual Studio, which is the compiler used to build the official Python
releases. These files are in the <code class="file docutils literal notranslate"><span class="pre">PCbuild</span></code> directory.</p>
<p>Check <code class="file docutils literal notranslate"><span class="pre">PCbuild/readme.txt</span></code> for general information on the build process.</p>
<p>For extension modules, consult <a class="reference internal" href="../extending/windows.html#building-on-windows"><span class="std std-ref">Building C and C++ Extensions on Windows</span></a>.</p>
</section>
<section id="other-platforms">
<h2><span class="section-number">4.12. </span>Other Platforms<a class="headerlink" href="#other-platforms" title="Permalink to this headline">¶</a></h2>
<p>With ongoing development of Python, some platforms that used to be supported
earlier are no longer supported (due to the lack of users or developers).
Check <span class="target" id="index-38"></span><a class="pep reference external" href="https://peps.python.org/pep-0011/"><strong>PEP 11</strong></a> for details on all unsupported platforms.</p>
<ul class="simple">
<li><p><a class="reference external" href="https://pythonce.sourceforge.net/">Windows CE</a> is
<a class="reference external" href="https://github.com/python/cpython/issues/71542">no longer supported</a>
since Python 3 (if it ever was).</p></li>
<li><p>The <a class="reference external" href="https://cygwin.com/">Cygwin</a> installer offers to install the
<a class="reference external" href="https://cygwin.com/packages/summary/python3.html">Python interpreter</a>
as well</p></li>
</ul>
<p>See <a class="reference external" href="https://www.python.org/downloads/windows/">Python for Windows</a>
for detailed information about platforms with pre-compiled installers.</p>
</section>
</section>


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    <ul>
<li><a class="reference internal" href="#">4. Using Python on Windows</a><ul>
<li><a class="reference internal" href="#the-full-installer">4.1. The full installer</a><ul>
<li><a class="reference internal" href="#installation-steps">4.1.1. Installation steps</a></li>
<li><a class="reference internal" href="#removing-the-max-path-limitation">4.1.2. Removing the MAX_PATH Limitation</a></li>
<li><a class="reference internal" href="#installing-without-ui">4.1.3. Installing Without UI</a></li>
<li><a class="reference internal" href="#installing-without-downloading">4.1.4. Installing Without Downloading</a></li>
<li><a class="reference internal" href="#modifying-an-install">4.1.5. Modifying an install</a></li>
</ul>
</li>
<li><a class="reference internal" href="#the-microsoft-store-package">4.2. The Microsoft Store package</a><ul>
<li><a class="reference internal" href="#known-issues">4.2.1. Known issues</a><ul>
<li><a class="reference internal" href="#redirection-of-local-data-registry-and-temporary-paths">4.2.1.1. Redirection of local data, registry, and temporary paths</a></li>
</ul>
</li>
</ul>
</li>
<li><a class="reference internal" href="#the-nuget-org-packages">4.3. The nuget.org packages</a></li>
<li><a class="reference internal" href="#the-embeddable-package">4.4. The embeddable package</a><ul>
<li><a class="reference internal" href="#python-application">4.4.1. Python Application</a></li>
<li><a class="reference internal" href="#embedding-python">4.4.2. Embedding Python</a></li>
</ul>
</li>
<li><a class="reference internal" href="#alternative-bundles">4.5. Alternative bundles</a></li>
<li><a class="reference internal" href="#configuring-python">4.6. Configuring Python</a><ul>
<li><a class="reference internal" href="#excursus-setting-environment-variables">4.6.1. Excursus: Setting environment variables</a></li>
<li><a class="reference internal" href="#finding-the-python-executable">4.6.2. Finding the Python executable</a></li>
</ul>
</li>
<li><a class="reference internal" href="#utf-8-mode">4.7. UTF-8 mode</a></li>
<li><a class="reference internal" href="#python-launcher-for-windows">4.8. Python Launcher for Windows</a><ul>
<li><a class="reference internal" href="#getting-started">4.8.1. Getting started</a><ul>
<li><a class="reference internal" href="#from-the-command-line">4.8.1.1. From the command-line</a></li>
<li><a class="reference internal" href="#virtual-environments">4.8.1.2. Virtual environments</a></li>
<li><a class="reference internal" href="#from-a-script">4.8.1.3. From a script</a></li>
<li><a class="reference internal" href="#from-file-associations">4.8.1.4. From file associations</a></li>
</ul>
</li>
<li><a class="reference internal" href="#shebang-lines">4.8.2. Shebang Lines</a></li>
<li><a class="reference internal" href="#arguments-in-shebang-lines">4.8.3. Arguments in shebang lines</a></li>
<li><a class="reference internal" href="#customization">4.8.4. Customization</a><ul>
<li><a class="reference internal" href="#customization-via-ini-files">4.8.4.1. Customization via INI files</a></li>
<li><a class="reference internal" href="#customizing-default-python-versions">4.8.4.2. Customizing default Python versions</a></li>
</ul>
</li>
<li><a class="reference internal" href="#diagnostics">4.8.5. Diagnostics</a></li>
<li><a class="reference internal" href="#dry-run">4.8.6. Dry Run</a></li>
<li><a class="reference internal" href="#install-on-demand">4.8.7. Install on demand</a></li>
<li><a class="reference internal" href="#return-codes">4.8.8. Return codes</a></li>
</ul>
</li>
<li><a class="reference internal" href="#finding-modules">4.9. Finding modules</a></li>
<li><a class="reference internal" href="#additional-modules">4.10. Additional modules</a><ul>
<li><a class="reference internal" href="#pywin32">4.10.1. PyWin32</a></li>
<li><a class="reference internal" href="#cx-freeze">4.10.2. cx_Freeze</a></li>
</ul>
</li>
<li><a class="reference internal" href="#compiling-python-on-windows">4.11. Compiling Python on Windows</a></li>
<li><a class="reference internal" href="#other-platforms">4.12. Other Platforms</a></li>
</ul>
</li>
</ul>

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