86 lines
2.2 KiB
Plaintext
86 lines
2.2 KiB
Plaintext
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This rule raises an issue when a `TypeVar` is used as a type parameter in a `type` statement.
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== Why is this an issue?
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Prior to Python 3.12, generic type aliases were defined as follows:
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[source,python]
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----
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from typing import TypeAlias, TypeVar
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_T = TypeVar("_T")
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MyAlias: TypeAlias = set[_T]
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----
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Python 3.12 introduced the `type` statement to facilitate the use of such type aliases,
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allowing for less confusing and more concise code:
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[source,python]
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----
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type MyAlias[T] = set[T]
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----
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Python is transitioning away from explicit `TypeVar` declaration from Python 3.12 onward.
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This means that Type alias expressions are not allowed to use `TypeVar` allocated with an explicit constructor call:
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[source,python]
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----
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from typing import TypeVar
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_T = TypeVar("_T")
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type MyAlias[A: str] = dict[A, _T] # Type checker error would be raise
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----
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It is a good practice to use the new syntax only, as it fulfills all the requirements of the `TypeVar` declaration in a more concise and readable way.
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=== Exceptions
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This rule will only raise an issue when the Python version of the analyzed project is set to 3.12 or higher.
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== How to fix it
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To fix this error use a generic `type` statement and remove the use of the `TypeVar`.
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=== Code examples
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==== Noncompliant code example
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[source,python,diff-id=1,diff-type=noncompliant]
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----
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from typing import TypeAlias
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_T = TypeVar("_T")
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type MyAlias = set[_T] # Noncompliant: a TypeVar is used as part of the type statement
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----
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==== Compliant solution
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[source,python,diff-id=1,diff-type=compliant]
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----
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type MyAlias[T] = set[T] # Compliant: the new type statement syntax is used.
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----
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== Resources
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=== Documentation
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* Python Documentation - https://docs.python.org/3.12/reference/simple_stmts.html#type[The type statement]
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* Python 3.12 Release Notes - https://docs.python.org/3.12/whatsnew/3.12.html#pep-695-type-parameter-syntax[PEP 695: Type Parameter Syntax]
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* PEP 695 - https://peps.python.org/pep-0695/[Type Parameter Syntax]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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=== Message
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(visible only on this page)
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Use a generic type parameter instead of a `TypeVar` in this `type` statement.
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'''
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endif::env-github,rspecator-view[]
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