bpo-44796: Unify TypeVar and ParamSpec substitution #31143
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Add methods __typing_subst__() in TypeVar and ParamSpec.
JelleZijlstra
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JelleZijlstra
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Thanks, this does make things simpler, but we need to be careful that we don't break too many external consumers of typing code. Also, there may be interactions with #31021, which adds another TypeVar variant.
Here's a few comments, but I may need to look at this more to understand it better.
| f"ParamSpec, or Concatenate. Got {t_args}") | ||
| return super().__new__(cls, origin, args) | ||
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| @property |
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I think we have to keep __parameters__, it's de facto a public API by now.
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It is inherited from GenericAlias now.
Lib/typing.py
Outdated
| if isinstance(arg, _SpecialForm) or arg in (Generic, Protocol): | ||
| raise TypeError(f"Plain {arg} is not valid as type argument") | ||
| if isinstance(arg, (type, TypeVar, ForwardRef, types.UnionType, ParamSpec)): | ||
| if isinstance(arg, (type, TypeVar, ForwardRef, types.UnionType)): |
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Will this affect putting ParamSpec inside Annotated? Looks like we don't have tests for that yet.
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I looked into this.
This check is needed in order to allow instances of ParamSpec (i.e. P in P = ParamSpec("P")) to pass typing._type_check because callable(P) is False. This can show up for instance like Callable[Annotated[P, ""], T]. This line's change would regress the behavior to a runtime error.
n.b. this is moot if #31151 gets merged since this line is removed entirely
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Callable[Annotated[P, ""], T] does not conform the PEP 612 specification.
callable ::= Callable "[" parameters_expression, type_expression "]"
parameters_expression ::=
| "..."
| "[" [ type_expression ("," type_expression)* ] "]"
| parameter_specification_variable
| concatenate "["
type_expression ("," type_expression)* ","
parameter_specification_variable
"]"
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I'm not convinced it was the intent of the spec here to disallow Annotated, but you can also reach this code here:
from typing import Callable, TypeVar, ParamSpec, get_type_hints
T = TypeVar("T")
P = ParamSpec("P")
def add_logging(f: Callable["P", T]):
pass
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Well, I re-added ParamSpec. Now some errors will not be caught at runtime. We will return to this in future.
| and _is_unpacked_typevartuple(old_arg)): | ||
| if _is_unpacked_typevartuple(old_arg): | ||
| original_typevartuple = old_arg.__parameters__[0] | ||
| new_arg = new_arg_by_param[original_typevartuple] |
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This code is not covered by tests.
It perhaps could be simplified too, but since it is not covered by tests I left it as is.
serhiy-storchaka
requested review from
Fidget-Spinner,
gvanrossum and
rhettinger
as code owners
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It now includes PEP 646 changes. |
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Did anyone review this? |
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Sorry, it was not reviewed after the last changes. But I addressed previous review comments. Is there something wrong with this code? I merged this PR after short delay because it allows the C code for TypeVarTuple substitution (#31828) to be of reasonable complexity. |
6 participants
Add methods typing_subst() in TypeVar and ParamSpec.
This is an alternative to #27511.
https://bugs.python.org/issue44796