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TopologicalSorter is not Generic at runtime (but is in typeshed) #89522

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JacobHayes mannequin opened this issue Oct 3, 2021 · 7 comments
Closed

TopologicalSorter is not Generic at runtime (but is in typeshed) #89522

JacobHayes mannequin opened this issue Oct 3, 2021 · 7 comments
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3.11 bug and security fixes stdlib Python modules in the Lib dir type-feature A feature request or enhancement

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@JacobHayes
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JacobHayes mannequin commented Oct 3, 2021

BPO 45359
Nosy @asvetlov, @AlexWaygood, @JacobHayes
PRs
  • bpo-45359: Support TopologicalSorter type subscript #28714
  • Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
    closed_at = <Date 2021-12-09.11:36:14.329>
    created_at = <Date 2021-10-03.22:18:50.416>
    labels = ['type-feature', 'library', '3.11']
    title = 'TopologicalSorter is not Generic at runtime (but is in typeshed)'
    updated_at = <Date 2021-12-10.14:59:57.694>
    user = 'https://github.com/JacobHayes'

    bugs.python.org fields:

    activity = <Date 2021-12-10.14:59:57.694>
    actor = 'JacobHayes'
    assignee = 'none'
    closed = True
    closed_date = <Date 2021-12-09.11:36:14.329>
    closer = 'asvetlov'
    components = ['Library (Lib)']
    creation = <Date 2021-10-03.22:18:50.416>
    creator = 'JacobHayes'
    dependencies = []
    files = []
    hgrepos = []
    issue_num = 45359
    keywords = ['patch']
    message_count = 7.0
    messages = ['403115', '408041', '408109', '408110', '408117', '408177', '408211']
    nosy_count = 3.0
    nosy_names = ['asvetlov', 'AlexWaygood', 'JacobHayes']
    pr_nums = ['28714']
    priority = 'normal'
    resolution = 'fixed'
    stage = 'resolved'
    status = 'closed'
    superseder = None
    type = 'enhancement'
    url = 'https://bugs.python.org/issue45359'
    versions = ['Python 3.11']

    @JacobHayes
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    JacobHayes mannequin commented Oct 3, 2021

    Reproduction:

    from graphlib import TopologicalSorter
    
    TopologicalSorter[str]({"a": {}, "b": {"a"}})
    
    $ mypy /tmp/toposort.py
    Success: no issues found in 1 source file
    $ python3 /tmp/toposort.py
    Traceback (most recent call last):
      File "/tmp/toposort.py", line 3, in <module>
        TopologicalSorter[str]({"a": {}, "b": {"a"}})
    TypeError: 'type' object is not subscriptable
    

    I opened the issue here (rather than typeshed) because we'd presumably like to support this at runtime too.

    Typeshed link: https://github.com/python/mypy/blob/0a830481980bfc554ded61a3eaaaecde384a21e4/mypy/typeshed/stdlib/graphlib.pyi#L6

    @JacobHayes JacobHayes mannequin added 3.9 only security fixes type-bug An unexpected behavior, bug, or error stdlib Python modules in the Lib dir labels Oct 3, 2021
    @AlexWaygood AlexWaygood added 3.10 only security fixes 3.11 bug and security fixes labels Nov 1, 2021
    @asvetlov
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    asvetlov commented Dec 8, 2021

    New changeset 3cb9731 by Jacob Hayes in branch 'main':
    bpo-45359: Support TopologicalSorter type subscript (GH-28714)
    3cb9731

    @asvetlov
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    asvetlov commented Dec 9, 2021

    The new feature is applied to Python 3.11 only

    @asvetlov asvetlov removed 3.9 only security fixes 3.10 only security fixes labels Dec 9, 2021
    @asvetlov asvetlov closed this as completed Dec 9, 2021
    @asvetlov asvetlov removed 3.9 only security fixes 3.10 only security fixes labels Dec 9, 2021
    @asvetlov asvetlov closed this as completed Dec 9, 2021
    @JacobHayes
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    JacobHayes mannequin commented Dec 9, 2021

    Thanks for merging!

    Should typeshed be updated for <3.11 in the meantime or do you suggest if TYPE_CHECKING blocks on user side? Perhaps it's a non-issue if no one else has noticed this. :)

    @asvetlov
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    asvetlov commented Dec 9, 2021

    `if TYPE_CHECKING:` is a good choice, it works fine just now.
    `from __future__ import annotations` is another alternative.

    I don't see a reason for REMOVING already existing and correct annotations from typeshed.

    @AlexWaygood
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    Another option for code using Python <3.11, that will work without the from __future__ import annotations import, is to do something like this:

    from graphlib import TopologicalSorter
    x: 'TopologicalSorter[str]' = TopologicalSorter({"a": {}, "b": {"a"}})
    

    By using a string as the annotation, we give mypy the specificity it needs, but the expression will never need to be resolved at runtime.

    @AlexWaygood AlexWaygood added type-feature A feature request or enhancement and removed type-bug An unexpected behavior, bug, or error labels Dec 10, 2021
    @JacobHayes
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    JacobHayes mannequin commented Dec 10, 2021

    Thanks for the tips! I've been using this patch in my own code in a early imported __init__.py:

    from graphlib import TopologicalSorter
    from types import GenericAlias
    
    if not hasattr(TopologicalSorter, "__class_getitem__"):  # pragma: no cover
        TopologicalSorter.__class_getitem__ = classmethod(GenericAlias)  # type: ignore
    

    Certainly a bit hacky, but aside from no-op on >=3.11 and satisfying mypy, it supports runtime type inspection via get_type_hints before 3.11 (which otherwise still errors for stringized versions). The stringized versions are probably a bit simpler/safer for most folks though :)

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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