Capsules

Refer to Providing a C API for an Extension Module for more information on using these objects.

New in version 3.1.

type PyCapsule

This subtype of PyObject represents an opaque value, useful for C extension modules who need to pass an opaque value (as a void* pointer) through Python code to other C code. It is often used to make a C function pointer defined in one module available to other modules, so the regular import mechanism can be used to access C APIs defined in dynamically loaded modules.

type PyCapsule_Destructor

Part of the Stable ABI.

The type of a destructor callback for a capsule. Defined as:

typedef void (*PyCapsule_Destructor)(PyObject *);

See PyCapsule_New() for the semantics of PyCapsule_Destructor callbacks.

int PyCapsule_CheckExact(PyObject *p)

Return true if its argument is a PyCapsule. This function always succeeds.

PyObject *PyCapsule_New(void *pointer, const char *name, PyCapsule_Destructor destructor)

Return value: New reference. Part of the Stable ABI.

Create a PyCapsule encapsulating the pointer. The pointer argument may not be NULL.

On failure, set an exception and return NULL.

The name string may either be NULL or a pointer to a valid C string. If non-NULL, this string must outlive the capsule. (Though it is permitted to free it inside the destructor.)

If the destructor argument is not NULL, it will be called with the capsule as its argument when it is destroyed.

If this capsule will be stored as an attribute of a module, the name should be specified as modulename.attributename. This will enable other modules to import the capsule using PyCapsule_Import().

void *PyCapsule_GetPointer(PyObject *capsule, const char *name)

Part of the Stable ABI.

Retrieve the pointer stored in the capsule. On failure, set an exception and return NULL.

The name parameter must compare exactly to the name stored in the capsule. If the name stored in the capsule is NULL, the name passed in must also be NULL. Python uses the C function strcmp() to compare capsule names.

PyCapsule_Destructor PyCapsule_GetDestructor(PyObject *capsule)

Part of the Stable ABI.

Return the current destructor stored in the capsule. On failure, set an exception and return NULL.

It is legal for a capsule to have a NULL destructor. This makes a NULL return code somewhat ambiguous; use PyCapsule_IsValid() or PyErr_Occurred() to disambiguate.

void *PyCapsule_GetContext(PyObject *capsule)

Part of the Stable ABI.

Return the current context stored in the capsule. On failure, set an exception and return NULL.

It is legal for a capsule to have a NULL context. This makes a NULL return code somewhat ambiguous; use PyCapsule_IsValid() or PyErr_Occurred() to disambiguate.

const char *PyCapsule_GetName(PyObject *capsule)

Part of the Stable ABI.

Return the current name stored in the capsule. On failure, set an exception and return NULL.

It is legal for a capsule to have a NULL name. This makes a NULL return code somewhat ambiguous; use PyCapsule_IsValid() or PyErr_Occurred() to disambiguate.

void *PyCapsule_Import(const char *name, int no_block)

Part of the Stable ABI.

Import a pointer to a C object from a capsule attribute in a module. The name parameter should specify the full name to the attribute, as in module.attribute. The name stored in the capsule must match this string exactly.

Return the capsule’s internal pointer on success. On failure, set an exception and return NULL.

Changed in version 3.3: no_block has no effect anymore.

int PyCapsule_IsValid(PyObject *capsule, const char *name)

Part of the Stable ABI.

Determines whether or not capsule is a valid capsule. A valid capsule is non-NULL, passes PyCapsule_CheckExact(), has a non-NULL pointer stored in it, and its internal name matches the name parameter. (See PyCapsule_GetPointer() for information on how capsule names are compared.)

In other words, if PyCapsule_IsValid() returns a true value, calls to any of the accessors (any function starting with PyCapsule_Get) are guaranteed to succeed.

Return a nonzero value if the object is valid and matches the name passed in. Return 0 otherwise. This function will not fail.

int PyCapsule_SetContext(PyObject *capsule, void *context)

Part of the Stable ABI.

Set the context pointer inside capsule to context.

Return 0 on success. Return nonzero and set an exception on failure.

int PyCapsule_SetDestructor(PyObject *capsule, PyCapsule_Destructor destructor)

Part of the Stable ABI.

Set the destructor inside capsule to destructor.

Return 0 on success. Return nonzero and set an exception on failure.

int PyCapsule_SetName(PyObject *capsule, const char *name)

Part of the Stable ABI.

Set the name inside capsule to name. If non-NULL, the name must outlive the capsule. If the previous name stored in the capsule was not NULL, no attempt is made to free it.

Return 0 on success. Return nonzero and set an exception on failure.

int PyCapsule_SetPointer(PyObject *capsule, void *pointer)

Part of the Stable ABI.

Set the void pointer inside capsule to pointer. The pointer may not be NULL.

Return 0 on success. Return nonzero and set an exception on failure.