typing.NamedTuple is used in two ways.

1. It is a callable which produces a new namedtuple type.
2. It can also be used as a base in the class statement for creating a new namedtuple type.

In both cases it is not a real class. You cannot create an instance of NamedTuple or a subclass of NamedTuple. But it is implemented as a class, and help() shows methods and data descriptors for it, which are useless.

The proposed PR implements NamedTuple like a function. Implementation of the __mro_entries__ method allows to use it as a base in the class statement.

See also issue40187.

New changeset a2ec06938f46683e33692615aca3875d8b8e110c by Serhiy Storchaka in branch 'master':
bpo-40185: Refactor typing.NamedTuple (GH-19371)
https://github.com/python/cpython/commit/a2ec06938f46683e33692615aca3875d8b8e110c

This seems to have caused a test failure in astroid project. I am not sure if the fix needs to be done from their end probably relying on some implementation detail or from the patch itself. Feel free to ignore if it's a third-party only error.

Reproducer script : /tmp/namedtuple_astroid.py

from astroid import parse

mod = parse('''from typing import NamedTuple; NamedTuple("A")''')
print(str(next(mod.body[-1].value.infer())))
assert str(next(mod.body[-1].value.infer())) != 'Uninferable'

Before this commit : 

python /tmp/namedtuple_astroid.py
Instance of typing.NamedTuple

After this commit : 

python /tmp/namedtuple_astroid.py
Uninferable
Traceback (most recent call last):
  File "/tmp/namedtuple_astroid.py", line 4, in <module>
    assert str(next(mod.body[-1].value.infer())) != 'Uninferable'
AssertionError

$ echo 'from typing import NamedTuple; NamedTuple("A")' | ./python -m ast
Module(
   body=[
      ImportFrom(
         module='typing',
         names=[
            alias(name='NamedTuple')],
         level=0),
      Expr(
         value=Call(
            func=Name(id='NamedTuple', ctx=Load()),
            args=[
               Constant(value='A')],
            keywords=[]))],
   type_ignores=[])

So mod.body[-1].value is a call:

    Call(func=Name(id='NamedTuple', ctx=Load()), args=[Constant(value='A')], keywords=[])

I do not know what Astroid does with this node, but seem the problem is in its infer() method.

pull_requests: + pull_request29885

pull_requests: + pull_request29799