Making decorators with optional arguments [duplicate]

Answer 1

Here is an other solution that work also if the optional argument is a callable:

def test_equal(func=None, optional_value=None):
    if func is not None and optional_value is not None:
        # prevent user to set func parameter manually
        raise ValueError("Don't set 'func' parameter manually")
    if optional_value is None:
        optional_value = 10  # The default value (if needed)

    def inner(function):
        def func_wrapper(*args, **kwargs):
            # do something
            return function(*args, **kwargs) == optional_value

        return func_wrapper

    if not func:
        return inner
    return inner(func)

This way both syntax will work:

@test_equal
def does_return_10():
    return 10

@test_equal(optional_value=20)
def does_return_20():
    return 20

# does_return_10() return True
# does_return_20() return True