Use a sentinel for missing __classcell__

Author: johnslavik

Lib/collections/__init__.py

@@ -358,7 +358,9 @@ def __ror__(self, other):
 except ImportError:
     _tuplegetter = lambda index, doc: property(_itemgetter(index), doc=doc)
 
-def _namedtuple(typename, field_names, *, rename=False, defaults=None, module=None, classcell=None):
+_nmtuple_classcell_sentinel = object()
+
+def _namedtuple(typename, field_names, *, rename=False, defaults=None, module=None, classcell=_nmtuple_classcell_sentinel):
     # Validate the field names.  At the user's option, either generate an error
     # message or automatically replace the field name with a valid name.
     if isinstance(field_names, str):
@@ -486,7 +488,7 @@ def __getnewargs__(self):
         '__match_args__': field_names,
     }
 
-    if classcell is not None:
+    if classcell is not _nmtuple_classcell_sentinel:
         class_namespace["__classcell__"] = classcell
 
     for index, name in enumerate(field_names):

Lib/typing.py

@@ -2929,7 +2929,7 @@ def __round__(self, ndigits: int = 0) -> T:
         pass
 
 
-def _make_nmtuple(name, fields, annotate_func, module, defaults = (), classcell=None):
+def _make_nmtuple(name, fields, annotate_func, module, defaults = (), classcell=collections._nmtuple_classcell_sentinel):
     nm_tpl = collections._namedtuple(name, fields, defaults=defaults,
                                      module=module, classcell=classcell)
     nm_tpl.__annotate__ = nm_tpl.__new__.__annotate__ = annotate_func
@@ -3000,7 +3000,7 @@ def annotate(format):
                                 f"{', '.join(default_names)}")
         nm_tpl = _make_nmtuple(typename, field_names, annotate,
                                defaults=[ns[n] for n in default_names], module=ns['__module__'],
-                               classcell=ns.pop('__classcell__', None))
+                               classcell=ns.pop('__classcell__', collections._nmtuple_classcell_sentinel))
         nm_tpl.__bases__ = bases
         if Generic in bases:
             class_getitem = _generic_class_getitem