Add support for collections.namedtuple #460

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1. rockneurotiko commented on Sep 16, 2014

   

   rockneurotiko

   on Sep 16, 2014

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   It's not implemented yet.
   Code
2. JukkaL

   added

   feature

   on Sep 22, 2014
3. JukkaL

   changed the title [-]Fails with collections.namedtuple[/-] [+]Add support for collections.namedtuple[/+] on Sep 22, 2014
4. akaihola commented on Oct 10, 2014

   

   akaihola

   on Oct 10, 2014

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   I now noticed that some work-arounds are mentioned in the "Common issues" section of the "Creating stubs for Python modules" wiki page.
5. JukkaL

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   on Nov 8, 2014
6. JukkaL commented on Nov 8, 2014

   

   JukkaL

   on Nov 8, 2014

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   The most primitive support would allow basic type checking with implicit Any item types:

   X = namedtuple('X', ['a', 'b'])
   x = X(1, 'x')  # Ok
   x.c  # Type error
   x.a + [1]  # No error, since a has implicit type Any

   We also need to support namedtuple as a base class:

   class X(namedtuple('X', ['a', 'b'])):
       ...

   The above features would allow running mypy on code that uses named tuples and perform rudimentary type checking.

   The next step (potentially as a separate issue) would be to allow specifying item types. Here is a potential syntax:

   X = namedtuple('X', ['a', 'b'])  # type: (int, str)

   Coming up with a syntax for the base class case is more difficult. Suggestions are welcome, or we can require the code to be rewritten like this:

   X = namedtuple('X', ['a', 'b'])  # type: (int, str)
   class X(X):
       ...
7. JukkaL commented on Nov 30, 2014

   

   JukkaL

   on Nov 30, 2014

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   I'm working on this.
8. JukkaL commented on Dec 1, 2014

   

   JukkaL

   on Dec 1, 2014

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   I just pushed an experimental, partial implementation of namedtuple support.

   This is supported:

   from collections import namedtuple
   X = namedtuple('X', ['a', 'b'])
   x = X(1, 'x')  # Ok
   x = X(1, c='x')  # Error
   x.c  # Error
   x.a + [1]  # No error, since a has implicit type Any
   class Y(X): 
       """you can use a namedtuple class as a base class"""

   Also, you can define the types of named tuple items using typing.NamedTuple:

   from typing import NamedTuple
   X = NamedTuple('X', [('a', int), ('b', str)])
   x = X(1, 'x')  # Ok
   x = X(1, 2)  # Error

   A bunch of stuff is still broken or unsupported, but this should be good enough for (most) library stubs that need namedtuple. I'm going to continue working on this.
9. JukkaL commented on Dec 18, 2014

   

   JukkaL

   on Dec 18, 2014

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   This is now implemented. It's not quite perfect yet, but it should be usable and I'll file issues for the remaining limitations (or just fix them).

   Now you can also use named tuples in the base class list:

   from typing import NamedTuple
   class Foo(NamedTuple('Bar', [('item1', int), ('item2', str)])):    # OK!
       ...
10. JukkaL

    closed this as completedon Dec 18, 2014
11. gvanrossum commented on Jan 7, 2015

    

    gvanrossum

    on Jan 7, 2015

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    I don't see NamedTuple defined in the https://github.com/JukkaL/typing project yet. mypy's own typing.py seems to have diverged (e.g. it has Callable, mypy still has Function, but mypy has NamedTuple).
13. JukkaL commented on May 12, 2015

    

    JukkaL

    on May 12, 2015

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    Yeah, the namedtuple implementation is missing a few things. Added a new issue: #661