optype.test

The type-check only optype.test module provides utilities for testing static types. It can only be used in if TYPE_CHECKING: blocks in .py files, or in .pyi files — it doesn't exist at runtime.

assert_subtype

The optype.test module currently only contains the assert_subtype function, which checks that a value is a subtype of (or assignable to) a given type. It can be seen as a flexible alternative to typing.assert_type, that allows for writing type-tests that are compatible with multiple type checkers.

For example, different type checkers may infer the literal 1 as int or Literal[1], causing assert_type(1, int) to be accepted by one type checker but not the other. In contrast, assert_subtype[int](1) will be accepted by both type checkers.

import optype as op

op.test.assert_subtype[int](True) # (1)!
op.test.assert_subtype[int](1) # (2)!
op.test.assert_subtype[int](1.0) # (3)!