Refactor typing.NamedTuple #84366

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1. serhiy-storchaka commented on Apr 4, 2020

   

   serhiy-storchaka

   on Apr 4, 2020

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   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.

   👍React with 👍1Reacted by Bartosz Sławecki
2. serhiy-storchaka

   added

   3.9 (EOL)end of lifeend of life

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   type-featureA feature request or enhancementA feature request or enhancement

   on Apr 4, 2020
3. serhiy-storchaka commented on Apr 4, 2020

   

   serhiy-storchaka

   on Apr 4, 2020

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   See also bpo-40187.
4. serhiy-storchaka commented on Apr 8, 2020

   

   serhiy-storchaka

   on Apr 8, 2020

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   New changeset a2ec069 by Serhiy Storchaka in branch 'master':
   bpo-40185: Refactor typing.NamedTuple (GH-19371)
   a2ec069
5. serhiy-storchaka

   closed this as completedon Apr 8, 2020
6. tirkarthi commented on Aug 10, 2020

   

   tirkarthi

   on Aug 10, 2020

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   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
7. serhiy-storchaka commented on Aug 10, 2020

   

   serhiy-storchaka

   on Aug 10, 2020

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   $ 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.
8. ezio-melotti

   transferred this issue fromon Apr 10, 2022