bpo-40185: Refactor typing.NamedTuple

Lib/test/test_typing.py

@@ -3598,11 +3598,9 @@ def test_annotation_usage_with_default(self):
  self.assertEqual(CoolEmployeeWithDefault._field_defaults, dict(cool=0))
 
  with self.assertRaises(TypeError):
- exec("""
-class NonDefaultAfterDefault(NamedTuple):
- x: int = 3
- y: int
-""")
+ class NonDefaultAfterDefault(NamedTuple):
+ x: int = 3
+ y: int
 
  def test_annotation_usage_with_methods(self):
  self.assertEqual(XMeth(1).double(), 2)
@@ -3611,20 +3609,23 @@ def test_annotation_usage_with_methods(self):
  self.assertEqual(XRepr(1, 2) + XRepr(3), 0)
 
  with self.assertRaises(AttributeError):
- exec("""
-class XMethBad(NamedTuple):
- x: int
- def _fields(self):
- return 'no chance for this'
-""")
+ class XMethBad(NamedTuple):
+ x: int
+ def _fields(self):
+ return 'no chance for this'
 
  with self.assertRaises(AttributeError):
- exec("""
-class XMethBad2(NamedTuple):
- x: int
- def _source(self):
- return 'no chance for this as well'
-""")
+ class XMethBad2(NamedTuple):
+ x: int
+ def _source(self):
+ return 'no chance for this as well'
+
+ def test_multiple_inheritance(self):
+ class A:
+ pass
+ with self.assertRaises(TypeError):
+ class X(NamedTuple, A):
+ x: int
 
  def test_multiple_inheritance(self):
  class A:

Lib/typing.py

@@ -1701,53 +1701,44 @@ def __round__(self, ndigits: int = 0) -> T_co:
  pass
 
 
-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])
+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)
  # Prior to PEP 526, only _field_types attribute was assigned.
  # Now __annotations__ are used and _field_types is deprecated (remove in 3.9)
- nm_tpl.__annotations__ = nm_tpl._field_types = dict(types)
- try:
- nm_tpl.__module__ = sys._getframe(2).f_globals.get('__name__', '__main__')
- except (AttributeError, ValueError):
- pass
+ nm_tpl._field_types = types
+ nm_tpl.__annotations__ = nm_tpl.__new__.__annotations__ = types
  return nm_tpl
 
 
 # attributes prohibited to set in NamedTuple class syntax
-_prohibited = {'__new__', '__init__', '__slots__', '__getnewargs__',
- '_fields', '_field_defaults', '_field_types',
- '_make', '_replace', '_asdict', '_source'}
+_prohibited = frozenset({'__new__', '__init__', '__slots__', '__getnewargs__',
+  '_fields', '_field_defaults', '_field_types',
+  '_make', '_replace', '_asdict', '_source'})
 
 _special = {'__module__', '__name__', '__annotations__'}
 
 
 class NamedTupleMeta(type):
 
  def __new__(cls, typename, bases, ns):
- if ns.get('_root', False):
- return super().__new__(cls, typename, bases, ns)
- if len(bases) > 1:
- raise TypeError("Multiple inheritance with NamedTuple is not supported")
- assert bases[0] is NamedTuple
+ assert bases[0] is _NamedTuple
  types = ns.get('__annotations__', {})
- nm_tpl = _make_nmtuple(typename, types.items())
- defaults = []
- defaults_dict = {}
+ default_names = []
  for field_name in types:
  if field_name in ns:
- 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
+ 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__'])
  # update from user namespace without overriding special namedtuple attributes
  for key in ns:
  if key in _prohibited:
@@ -1757,7 +1748,7 @@ def __new__(cls, typename, bases, ns):
  return nm_tpl
 
 
-class NamedTuple(metaclass=NamedTupleMeta):
+def NamedTuple(typename, fields=None, /, **kwargs):
  """Typed version of namedtuple.
 
  Usage in Python versions >= 3.6::
@@ -1781,15 +1772,26 @@ class Employee(NamedTuple):
 
  Employee = NamedTuple('Employee', [('name', str), ('id', int)])
  """
- _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)
+ if fields is None:
+ fields = kwargs.items()
+ elif kwargs:
+ raise TypeError("Either list of fields or keywords"
+ " can be provided to NamedTuple, not both")
+ try:
+ module = sys._getframe(1).f_globals.get('__name__', '__main__')
+ except (AttributeError, ValueError):
+ module = None
+ return _make_nmtuple(typename, fields, module=module)
+
+_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
 
 
 def _dict_new(cls, /, *args, **kwargs):