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Clarify generic type parameter ordering by BHUVANSH855 · Pull Request #2289 · python/typing · GitHub

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Clarify generic type parameter ordering - #2289

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BHUVANSH855 wants to merge 4 commits into
python:mainfrom
BHUVANSH855:spec/type-parameter-order
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Clarify generic type parameter ordering#2289
BHUVANSH855 wants to merge 4 commits into
python:mainfrom
BHUVANSH855:spec/type-parameter-order

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BHUVANSH855 commented May 18, 2026

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Summary

Clarify how type parameter ordering is determined for generic classes.

This expands the existing wording in the generics spec to explicitly
cover:

  • Generic[...] base classes
  • parameterized Protocol[...] base classes
  • Python 3.12 generic class syntax

The updated wording also clarifies that a bare Protocol base class
does not affect type parameter ordering.

Closes #2059

srittau added the topic: typing spec For improving the typing spec label May 18, 2026

JelleZijlstra commented May 21, 2026

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@BHUVANSH855 please do not keep merging main into your branch unless there is an actual merge conflict.

JelleZijlstra requested changes May 21, 2026
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I think we should add a section header "Type parameter ordering", starting at line 487 or so. Currently this is in a section "Arbitrary generic types as base classes", which isn't really apposite.

Comment thread docs/spec/generics.rst Outdated
Comment thread docs/spec/generics.rst Outdated

JelleZijlstra commented May 21, 2026

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Also, is this already covered sufficiently in the conformance suite? What are the relevant tests that we have?

BHUVANSH855 commented May 21, 2026

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Also, is this already covered sufficiently in the conformance suite? What are the relevant tests that we have?

Addressed the requested changes:

  • added a dedicated “Type parameter ordering” section header
  • reordered the section so the Python 3.12 generic class syntax appears first
  • updated “both examples” to “all of the examples above”

There is already conformance coverage for Protocol[...] ordering in conformance/tests/protocols_generic.py. In particular, the Proto1(Iterable[T_co], Protocol[S, T_co]) example together with the specialization checks verifies that type parameter ordering follows the Protocol[...] subscript order.

This PR expands the spec wording to make the broader ordering rules explicit, including Generic[...], parameterized Protocol[...], bare Protocol, and PEP 695 syntax.

BHUVANSH855 requested a review from JelleZijlstra May 21, 2026 14:45
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Spec: More precision on type parameter order

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