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Add runtime generic alias support to datetime #161304

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Add runtime generic alias support to datetime#161304
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stdlibStandard Library Python modules in the Lib/ directorytopic-typingtype-featureA feature request or enhancement

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@m-aciek
m-aciek
opened on Nov 4, 2026

Feature or enhancement

@srittau has merged a PR with a support of parametrising datetime type with a timezone information in the typeshed. Allowing datetime to be a generic would let use that feature without workarounds in Python.

from datetime import datetime, UTC

global_now: datetime[UTC] = datetime.now(UTC)
local_now: datetime[None] = datetime.now()

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

python/typeshed#11844

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Activity

  1. m-aciek
    added
    type-featureA feature request or enhancement
    stdlibStandard Library Python modules in the Lib/ directory
    on Nov 4, 2026

  2. srittau commented on Nov 4, 2026

    @srittau
    srittau
    on Nov 4, 2026
    Contributor

    A few comments:

    • The typeshed change could be a huge help to detect (sometimes rather subtle) bugs with naïve vs tz-aware datetimes.
    • Nevertheless, the change is new and hasn't made it into any type checkers yet (as far as I'm aware). It might turn out to be too controversial and might need backing out in typeshed (although I hope not). So I would wait maybe 1-2 months with this to make sure we keep the change in typeshed.
    • That said, if we keep it, this would be quite helpful and would be in line with similar changes we've made to CPython.
  3. sobolevn
    added
    topic-typing
    on Nov 4, 2026

  4. sobolevn commented on Nov 4, 2026

    @sobolevn
    sobolevn
    on Nov 4, 2026
    Member

    What about datetime.time? It also has tzinfo parameter in some places:

    >>> import datetime
>>> datetime.time(4, 23, 1) == datetime.time(4, 23, 1, tzinfo=datetime.timezone.utc)
False

  5. srittau commented on Nov 4, 2026

    @srittau
    srittau
    on Nov 4, 2026
    Contributor

    What about datetime.time? It also has tzinfo parameter in some places:

    That seems ... weird. For consistency's sake, we should probably make it generic in typeshed and CPython, although I'm not sure what a time with a tzinfo parameter is even supposed to represent.

  6. StanFromIreland
    added this to Date and time issues 🕰️on Nov 4, 2026
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