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Forbid extra ParamSpec arguments #12024

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Merged
merged 2 commits into from
Jan 28, 2022
Merged

Forbid extra ParamSpec arguments #12024

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28755d8
Forbid extra `ParamSpec` arguments
sobolevn Jan 20, 2022
03fe8b8
Change error message
sobolevn Jan 28, 2022
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9 changes: 9 additions & 0 deletions mypy/semanal.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3292,6 +3292,15 @@ def process_paramspec_declaration(self, s: AssignmentStmt) -> bool:
if not self.check_typevarlike_name(call, name, s):
return False

# ParamSpec is different from a regular TypeVar:
# arguments are not semantically valid. But, allowed in runtime.
# So, we need to warn users about possible invalid usage.
if len(call.args) > 1:
self.fail(
"Only the first argument to ParamSpec has defined semantics",
s,
)

# PEP 612 reserves the right to define bound, covariant and contravariant arguments to
# ParamSpec in a later PEP. If and when that happens, we should do something
# on the lines of process_typevar_parameters
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10 changes: 10 additions & 0 deletions test-data/unit/check-parameter-specification.test
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Expand Up @@ -3,6 +3,16 @@ from typing_extensions import ParamSpec
P = ParamSpec('P')
[builtins fixtures/tuple.pyi]

[case testInvalidParamSpecDefinitions]
from typing import ParamSpec

P1 = ParamSpec("P1", covariant=True) # E: Only the first argument to ParamSpec has defined semantics
P2 = ParamSpec("P2", contravariant=True) # E: Only the first argument to ParamSpec has defined semantics
P3 = ParamSpec("P3", bound=int) # E: Only the first argument to ParamSpec has defined semantics
P4 = ParamSpec("P4", int, str) # E: Only the first argument to ParamSpec has defined semantics
P5 = ParamSpec("P5", covariant=True, bound=int) # E: Only the first argument to ParamSpec has defined semantics
[builtins fixtures/tuple.pyi]

[case testParamSpecLocations]
from typing import Callable, List
from typing_extensions import ParamSpec, Concatenate
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