negation types¶

not T in an annotation position is a type that excludes T:

def f(x: not int) -> None: ...

transpiles to:

from ty_extensions import Not

def f(x: Not[int]) -> None: ...

Not[T] is the basedpython type-system primitive for negation. it is sourced from ty_extensions and ty narrows accordingly: a value of type Not[int] will fail to type-check against int-typed positions

composition¶

not composes with | (union) and & (intersection) as well as nested generics:

precedence follows the source: parenthesize when the negation should bind across a union or intersection

scope¶

the rewrite fires only in syntactic annotation positions:

• function parameter annotations
• function return annotations
• variable annotations (x: not int)
• nested type arguments inside an annotation

not x in a value context — boolean negation — is never affected. the transform is structural, not type-aware