code: def _issubclass_Mapping_covariant(subclass, superclass, bound_Generic, bound_typevars,
              bound_typevars_readonly, follow_fwd_refs, _recursion_check):
      
      if is_Generic(subclass):
          if subclass.__origin__ is None or not issubclass(subclass.__origin__, Mapping):
              return _issubclass_Generic(subclass, superclass, bound_Generic, bound_typevars,
                      bound_typevars_readonly, follow_fwd_refs, _recursion_check)
          if superclass.__args__ is None:
              if not pytypes.check_unbound_types:
                  raise TypeError("Attempted to check unbound mapping type(superclass): "+
                          str(superclass))
              if pytypes.strict_unknown_check:
                  # Nothing is subtype of unknown type
                  return False
              super_args = (Any, Any)
          else:
              super_args = superclass.__args__
          if subclass.__args__ is None:
              if not pytypes.check_unbound_types:
                  raise TypeError("Attempted to check unbound mapping type(subclass): "+
                          str(subclass))
              if pytypes.strict_unknown_check:
                  # Nothing can subclass unknown type
                  # For value type it would be okay if superclass had Any as value type,
                  # as unknown type is subtype of Any. However, since key type is invariant
                  # and also unknown, it cannot pass.
                  return False
              sub_args = (Any, Any)
          else:
              sub_args = subclass.__args__
          if not _issubclass(sub_args[0], super_args[0],
                  bound_Generic, bound_typevars,
                  bound_typevars_readonly, follow_fwd_refs, _recursion_check):
              return False
          if not _issubclass(sub_args[1], super_args[1],
                  bound_Generic, bound_typevars,
                  bound_typevars_readonly, follow_fwd_refs, _recursion_check):
              return False
          return True
      return issubclass(subclass, superclass)
docs: Helper for _issubclass, a.k.a pytypes.issubtype.
      This subclass-check treats Mapping-values as covariant.