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## Summary There is a new official URL for the typing documentation: https://typing.python.org/ Change all https://typing.readthedocs.io/ links to use the new sub domain, which is slightly shorter and looks more official. ## Test Plan Tested to see if each and every new URL is accessible. I noticed that some links go to https://typing.python.org/en/latest/source/stubs.html which seems to be outdated, but that is a separate issue. The same page shows up for the old URL.
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Legacy type variables
The tests in this file focus on how type variables are defined using the legacy notation. Most uses of type variables are tested in other files in this directory; we do not duplicate every test for both type variable syntaxes.
Unless otherwise specified, all quotations come from the Generics section of the typing spec.
Type variables
Defining legacy type variables
Generics can be parameterized by using a factory available in
typingcalledTypeVar.
This was the only way to create type variables prior to PEP 695/Python 3.12. It is still available in newer Python releases.
from typing import TypeVar
T = TypeVar("T")
Directly assigned to a variable
A
TypeVar()expression must always directly be assigned to a variable (it should not be used as part of a larger expression).
from typing import TypeVar
# TODO: error
TestList = list[TypeVar("W")]
TypeVar parameter must match variable name
The argument to
TypeVar()must be a string equal to the variable name to which it is assigned.
from typing import TypeVar
# TODO: error
T = TypeVar("Q")
No redefinition
Type variables must not be redefined.
from typing import TypeVar
T = TypeVar("T")
# TODO: error
T = TypeVar("T")
Cannot have only one constraint
TypeVarsupports constraining parametric types to a fixed set of possible types...There should be at least two constraints, if any; specifying a single constraint is disallowed.
from typing import TypeVar
# TODO: error: [invalid-type-variable-constraints]
T = TypeVar("T", int)