    def redefine(self, type: str, fn) -> TypeChecker:
        """
        Produce a new checker with the given type redefined.

        Arguments:

            type:

                The name of the type to check.

            fn (collections.abc.Callable):

                A callable taking exactly two parameters - the type
                checker calling the function and the instance to check.
                The function should return true if instance is of this
                type and false otherwise.

        """
        return self.redefine_many({type: fn})
Produce a new checker with the given type redefined.

Arguments:

type:

The name of the type to check.

fn (collections.abc.Callable):

A callable taking exactly two parameters - the type
checker calling the function and the instance to check.
The function should return true if instance is of this
type and false otherwise.
jsonschema/_types.py