code: def _not_a_coeff(expr):
      """Do not treat NaN and infinities as valid polynomial coefficients."""
      if type(expr) in illegal_types or expr in finf:
          return True
      if isinstance(expr, float) and float(expr) != expr:
          return True  # nan
      return
  
imports: from __future__ import annotations
  from sympy.external.gmpy import GROUND_TYPES
  from sympy.core import S, Add, Mul, Pow, Eq, Expr, expand_mul, expand_multinomial
  from sympy.core.exprtools import decompose_power, decompose_power_rat
  from sympy.core.numbers import _illegal
  from sympy.polys.polyerrors import PolynomialError, GeneratorsError
  from sympy.polys.polyoptions import build_options
  import re
label_desc: Use image node_id 6 for calling a global function with example usage: _not_a_coeff(expr) and returns: True, True