code: def _issubclass_Union(subclass, superclass, bound_Generic, bound_typevars,
              bound_typevars_readonly, follow_fwd_refs, _recursion_check):
      
      if not follow_fwd_refs:
          return _issubclass_Union_rec(subclass, superclass, bound_Generic, bound_typevars,
              bound_typevars_readonly, follow_fwd_refs, _recursion_check)
      try:
          # try to succeed fast, before we go the expensive way involving recursion checks
          return _issubclass_Union_rec(subclass, superclass, bound_Generic, bound_typevars,
              bound_typevars_readonly, False, _recursion_check)
      except pytypes.ForwardRefError:
          return _issubclass_Union_rec(subclass, superclass, bound_Generic, bound_typevars,
              bound_typevars_readonly, follow_fwd_refs, _recursion_check)
docs: Helper for _issubclass, a.k.a pytypes.issubtype.