bpo-43923: Allow NamedTuple multiple inheritance

Lib/test/test_typing.py

@@ -4947,9 +4947,8 @@ def _source(self):
  def test_multiple_inheritance(self):
  class A:
  pass
- with self.assertRaises(TypeError):
- class X(NamedTuple, A):
- x: int
+ class X(NamedTuple, A):
+ x: int
 
  def test_namedtuple_keyword_usage(self):
  LocalEmployee = NamedTuple("LocalEmployee", name=str, age=int)
@@ -5282,6 +5281,11 @@ def test_get_type_hints(self):
  {'a': typing.Optional[int], 'b': int}
  )
 
+ def test_generic_subclasses(self):
+ T = TypeVar("T")
+ class GenericNamedTuple(NamedTuple, Generic[T]):
+ pass
+
 
 class IOTests(BaseTestCase):
 

Lib/typing.py

@@ -2595,13 +2595,15 @@ def __round__(self, ndigits: int = 0) -> T_co:
  pass
 
 
-def _make_nmtuple(name, types, module, defaults = ()):
- fields = [n for n, t in types]
- types = {n: _type_check(t, f"field {n} annotation must be a type")
- for n, t in types}
- nm_tpl = collections.namedtuple(name, fields,
- defaults=defaults, module=module)
- nm_tpl.__annotations__ = nm_tpl.__new__.__annotations__ = types
+def _make_nmtuple(name, types):
+ msg = "NamedTuple('Name', [(f0, t0), (f1, t1), ...]); each t must be a type"
+ types = [(n, _type_check(t, msg)) for n, t in types]
+ nm_tpl = collections.namedtuple(name, [n for n, t in types])
+ nm_tpl.__annotations__ = dict(types)
+ try:
+ nm_tpl.__module__ = sys._getframe(2).f_globals.get('__name__', '__main__')
+ except (AttributeError, ValueError):
+ pass
  return nm_tpl
 
 
@@ -2616,20 +2618,26 @@ def _make_nmtuple(name, types, module, defaults = ()):
 class NamedTupleMeta(type):
 
  def __new__(cls, typename, bases, ns):
- assert bases[0] is _NamedTuple
+ if ns.get('_root', False):
+ return super().__new__(cls, typename, bases, ns)
+ assert bases[0] is NamedTuple
  types = ns.get('__annotations__', {})
- default_names = []
+ nm_tpl = _make_nmtuple(typename, types.items())
+ defaults = []
+ defaults_dict = {}
  for field_name in types:
  if field_name in ns:
- default_names.append(field_name)
- elif default_names:
- raise TypeError(f"Non-default namedtuple field {field_name} "
- f"cannot follow default field"
- f"{'s' if len(default_names) > 1 else ''} "
- f"{', '.join(default_names)}")
- nm_tpl = _make_nmtuple(typename, types.items(),
- defaults=[ns[n] for n in default_names],
- module=ns['__module__'])
+ default_value = ns[field_name]
+ defaults.append(default_value)
+ defaults_dict[field_name] = default_value
+ elif defaults:
+ raise TypeError("Non-default namedtuple field {field_name} cannot "
+ "follow default field(s) {default_names}"
+ .format(field_name=field_name,
+ default_names=', '.join(defaults_dict.keys())))
+ nm_tpl.__new__.__annotations__ = dict(types)
+ nm_tpl.__new__.__defaults__ = tuple(defaults)
+ nm_tpl._field_defaults = defaults_dict
  # update from user namespace without overriding special namedtuple attributes
  for key in ns:
  if key in _prohibited:
@@ -2639,7 +2647,7 @@ def __new__(cls, typename, bases, ns):
  return nm_tpl
 
 
-def NamedTuple(typename, fields=None, /, **kwargs):
+class NamedTuple(metaclass=NamedTupleMeta):
  """Typed version of namedtuple.
 
  Usage in Python versions >= 3.6::
@@ -2663,22 +2671,15 @@ class Employee(NamedTuple):
 
  Employee = NamedTuple('Employee', [('name', str), ('id', int)])
  """
- if fields is None:
- fields = kwargs.items()
- elif kwargs:
- raise TypeError("Either list of fields or keywords"
- " can be provided to NamedTuple, not both")
- return _make_nmtuple(typename, fields, module=_caller())
-
-_NamedTuple = type.__new__(NamedTupleMeta, 'NamedTuple', (), {})
-
-def _namedtuple_mro_entries(bases):
- if len(bases) > 1:
- raise TypeError("Multiple inheritance with NamedTuple is not supported")
- assert bases[0] is NamedTuple
- return (_NamedTuple,)
-
-NamedTuple.__mro_entries__ = _namedtuple_mro_entries
+ _root = True
+
+ def __new__(cls, typename, fields=None, /, **kwargs):
+ if fields is None:
+ fields = kwargs.items()
+ elif kwargs:
+ raise TypeError("Either list of fields or keywords"
+ " can be provided to NamedTuple, not both")
+ return _make_nmtuple(typename, fields)
 
 
 class _TypedDictMeta(type):

Misc/NEWS.d/next/Library/2022-03-08-20-13-08.bpo-43923.gefhqh.rst

@@ -0,0 +1,2 @@
+Multiple inheritance with :class:`typing.NamedTuple` now no longer raises an
+error.