gh-138859: Account for ParamSpec defaults that are not lists …
#138868
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…when converting type argument list to tuple
bzoracler
requested review from
JelleZijlstra and
AlexWaygood
as code owners
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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool. If this change has little impact on Python users, wait for a maintainer to apply the |
Lib/typing.py
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| @@ -1110,6 +1110,8 @@ def _paramspec_prepare_subst(self, alias, args): | |||
| # Convert lists to tuples to help other libraries cache the results. | |||
| elif isinstance(args[i], list): | |||
| args = (*args[:i], tuple(args[i]), *args[i+1:]) | |||
| else: | |||
| args = (*args[:i], args[i], *args[i + 1:]) | |||
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this can be simplified to args = tuple(args)
| @@ -0,0 +1 @@ | |||
| Fix failure during parameterization of generics when a non-type-list `ParamSpec` default is followed by another type variable default, and the `ParamSpec` is not provided as a type argument. | |||
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We use rst, not md in NEWS, so please use double backticks.
Lib/typing.py
Outdated
| @@ -1110,6 +1110,8 @@ def _paramspec_prepare_subst(self, alias, args): | |||
| # Convert lists to tuples to help other libraries cache the results. | |||
| elif isinstance(args[i], list): | |||
| args = (*args[:i], tuple(args[i]), *args[i+1:]) | |||
| else: | |||
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Should we create a tuple directly on line 1103 above instead?
| @@ -0,0 +1 @@ | |||
| Fix failure during parameterization of generics when a non-type-list ``ParamSpec`` default is followed by another type variable default, and the ``ParamSpec`` is not provided as a type argument. | |||
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Sorry, I don't understand what "non-type-list" is. I propose this wording:
| Fix failure during parameterization of generics when a non-type-list ``ParamSpec`` default is followed by another type variable default, and the ``ParamSpec`` is not provided as a type argument. | |
| Fixes a :exc:`TypeError` when substituting a :class:`ParamSpec` with a default | |
| that is followed by another :class:`TypeVar` with a default. |
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Thanks, the original description was unclear. Unless there are other objections, I'll reduce it to
Fix generic type parameterization raising a :exc:
TypeErrorwhen omitting a :class:ParamSpecthat has a non-type-list default.
"Non-type-list default" refers to the bug occurring if the ParamSpec default isn't a list of types, such as ... or P (another ParamSpec in scope). The bug would not be encountered if the default was a list of types (like [int, str]).
I think the closest wording for this construct in the documentation is actually "list of types" (see e.g. ParamSpec Defaults), but I don't think "list of types" is necessarily better than "type list".
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Let's say something like "default that is not a list of types". "type list" is definitely less clear to me than "list of types".
…when converting type argument list to tuple
Allows omitting common
ParamSpecdefaults, like...or anotherParamSpec.ParamSpec(default=...)fails if not provided as a type argument and not in the last position of a type list when passing type arguments #138859ParamSpec(default=...)fails if not provided as a type argument and not in the last position of a type list when passing type arguments #138859