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non-pep604-annotation (UP007)#

Derived from the pyupgrade linter.

Fix is sometimes available.

What it does#

Check for type annotations that can be rewritten based on PEP 604 syntax.

Why is this bad?#

PEP 604 introduced a new syntax for union type annotations based on the | operator. This syntax is more concise and readable than the previous typing.Union and typing.Optional syntaxes.

This rule is enabled when targeting Python 3.10 or later (see: target-version). By default, it's also enabled for earlier Python versions if from __future__ import annotations is present, as __future__ annotations are not evaluated at runtime. If your code relies on runtime type annotations (either directly or via a library like Pydantic), you can disable this behavior for Python versions prior to 3.10 by setting lint.pyupgrade.keep-runtime-typing to true.


from typing import Union

foo: Union[int, str] = 1

Use instead:

foo: int | str = 1

Fix safety#

This rule's fix is marked as unsafe, as it may lead to runtime errors when alongside libraries that rely on runtime type annotations, like Pydantic, on Python versions prior to Python 3.10. It may also lead to runtime errors in unusual and likely incorrect type annotations where the type does not support the | operator.