code: def unify_walk(a, b, U):
      """
      Checks for the existence of the __unify_walk__ method for one of
      the objects.
  
      """
      if (
          not isinstance(a, Variable)
          and not isinstance(b, Variable)
          and hasattr(a, "__unify_walk__")
      ):
          return a.__unify_walk__(b, U)
      else:
          return FALL_THROUGH
  
imports: from __future__ import absolute_import, print_function, division
  from copy import copy
  from functools import partial
  from theano.gof.utils import ANY_TYPE, comm_guard, FALL_THROUGH, iteritems
label_desc: Use image node_id 15 for calling a global function with example usage: unify_walk(a, b, U) and returns: a, FALL_THROUGH