[New-bugs-announce] [issue35341] Add generic version of OrderedDict to typing module

[Ismo Toijala]

New submission from Ismo Toijala <ismo.toijala at gmail.com>:

The other collections from the collections module (namedtuple, deque, ChainMap, Counter, defaultdict) have generic versions in the typing module for use in type annotations.

The problem is currently the following:

from __future__ import annotations
import typing
from collections import OrderedDict
# Understood by mypy
def f(d: OrderedDict[str, str]) -> None:
    pass
typing.get_type_hints(f)

gives:

Traceback (most recent call last):
  File "foo.py", line 9, in <module>
    typing.get_type_hints(f)
  File "/usr/lib/python3.7/typing.py", line 1001, in get_type_hints
    value = _eval_type(value, globalns, localns)
  File "/usr/lib/python3.7/typing.py", line 260, in _eval_type
    return t._evaluate(globalns, localns)
  File "/usr/lib/python3.7/typing.py", line 464, in _evaluate
    eval(self.__forward_code__, globalns, localns),
  File "<string>", line 1, in <module>
TypeError: 'type' object is not subscriptable

To fix this, a line like the following could be added to Lib/typing.py near line 1250:

OrderedDict = _alias(collections.OrderedDict, (KT, VT))

There might be a reasoning for why this has not been done yet, but I have not been able to find any.

If this is acceptable, I could prepare a PR.
I suppose there is no hope of a backport to 3.7, since this is a new feature (though very minor).

----------
components: Library (Lib)
messages: 330616
nosy: itoijala
priority: normal
severity: normal
status: open
title: Add generic version of OrderedDict to typing module
type: enhancement
versions: Python 3.7, Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35341>
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