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- """
- A few practical conventions common to all printers.
- """
- import re
- from collections.abc import Iterable
- from sympy.core.function import Derivative
- _name_with_digits_p = re.compile(r'^([^\W\d_]+)(\d+)$', re.U)
- def split_super_sub(text):
- """Split a symbol name into a name, superscripts and subscripts
- The first part of the symbol name is considered to be its actual
- 'name', followed by super- and subscripts. Each superscript is
- preceded with a "^" character or by "__". Each subscript is preceded
- by a "_" character. The three return values are the actual name, a
- list with superscripts and a list with subscripts.
- Examples
- ========
- >>> from sympy.printing.conventions import split_super_sub
- >>> split_super_sub('a_x^1')
- ('a', ['1'], ['x'])
- >>> split_super_sub('var_sub1__sup_sub2')
- ('var', ['sup'], ['sub1', 'sub2'])
- """
- if not text:
- return text, [], []
- pos = 0
- name = None
- supers = []
- subs = []
- while pos < len(text):
- start = pos + 1
- if text[pos:pos + 2] == "__":
- start += 1
- pos_hat = text.find("^", start)
- if pos_hat < 0:
- pos_hat = len(text)
- pos_usc = text.find("_", start)
- if pos_usc < 0:
- pos_usc = len(text)
- pos_next = min(pos_hat, pos_usc)
- part = text[pos:pos_next]
- pos = pos_next
- if name is None:
- name = part
- elif part.startswith("^"):
- supers.append(part[1:])
- elif part.startswith("__"):
- supers.append(part[2:])
- elif part.startswith("_"):
- subs.append(part[1:])
- else:
- raise RuntimeError("This should never happen.")
- # Make a little exception when a name ends with digits, i.e. treat them
- # as a subscript too.
- m = _name_with_digits_p.match(name)
- if m:
- name, sub = m.groups()
- subs.insert(0, sub)
- return name, supers, subs
- def requires_partial(expr):
- """Return whether a partial derivative symbol is required for printing
- This requires checking how many free variables there are,
- filtering out the ones that are integers. Some expressions do not have
- free variables. In that case, check its variable list explicitly to
- get the context of the expression.
- """
- if isinstance(expr, Derivative):
- return requires_partial(expr.expr)
- if not isinstance(expr.free_symbols, Iterable):
- return len(set(expr.variables)) > 1
- return sum(not s.is_integer for s in expr.free_symbols) > 1
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