sympycore/heads/special.py

   1
   2 from .base import AtomicHead, heads_precedence, Expr
   3
   4 import re
   5 _is_atomic = re.compile(r'\A\w+\Z').match
   6
   7 class SpecialHead(AtomicHead):
   8     """
   9     SpecialHead is head for special objects like None, NotImplemented,
  10     Ellipsis, etc.  Data can be any Python object.
  11     """
  12
  13     def __repr__(self): return 'SPECIAL'
  14
  15     def data_to_str_and_precedence(self, cls, data):
  16         if isinstance(data, Expr):
  17             h, d = data.pair
  18             return h.data_to_str_and_precedence(cls, d)
  19         if data is Ellipsis:
  20             return '...', heads_precedence.SYMBOL
  21
  22         s = str(data)
  23         if _is_atomic(s):
  24             return s, heads_precedence.SYMBOL
  25         return s, 0.0 # force parenthesis
  26
  27 SPECIAL = SpecialHead()