Optional

This page documents the Optional checker.

class argscheck.optional.Optional(*args, default_value=<MISSING>, default_factory=<MISSING>, sentinel=None, **kwargs)

Check if x is None or something else, similarly to typing.Optional.

Parameters

• args – Tuple[CheckerLike] – Specifies what x may be (other than None).

• default_value – Optional[Any] – If x is None, it will be replaced by default_value.

• default_factory – Optional[Callable] – if x is None, it will be replaced by a value freshly returned from default_factory(). This is useful for setting default values that are of mutable types.

• sentinel – Optional[Any] – x is sentinel will be used to determine if the x is missing, instead of x is None.

Example

from argscheck import check, Optional


# Check if a list, set or None, replace None with a fresh list
checker = Optional(list, set, default_factory=list)

check(checker, [1, 2, 3])  # Passes, [1, 2, 3] is returned
check(checker, {1, 2, 3})  # Passes, {1, 2, 3} is returned
check(checker, None)       # Passes, [] is returned
check(checker, "string")   # Fails, a TypeError is raised