Rewrite Optional[Type] to Type | None Has Fix

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Description

PEP 604 recommends that Type | None is preferred over Optional[Type] for Python 3.10+.

This rule performs such rewriting. Note Optional[$T] alone is interpreted as subscripting expression instead of generic type, we need to use pattern object to disambiguate it with more context code.

YAML

id: optional-to-none-union
language: python
rule:
  pattern:
    context: 'a: Optional[$T]'
    selector: generic_type
fix: $T | None

Example

def a(arg: Optional[Int]): pass

Diff

def a(arg: Optional[Int]): pass
def a(arg: Int | None): pass

Contributed by

Bede Carroll