Python required variable style

Question

What is the best style for a Python method that requires the keyword argument 'required_arg':

def test_method(required_arg, *args, **kwargs):


def test_method(*args, **kwargs):
    required_arg = kwargs.pop('required_arg')
    if kwargs:
        raise ValueError('Unexpected keyword arguments: %s' % kwargs)

Or something else? I want to use this for all my methods in the future so I'm kind of looking for the best practices way to deal with required keyword arguments in Python methods.

Answer 1

The first method by far. Why duplicate something the language already provides for you?

Optional arguments in most cases should be known (only use *args and **kwargs when there is no possible way of knowing the arguments). Denote optional arguments by giving them their default value (def bar(foo = 0) or def bar(foo = None)). Watch out for the classic gotcha of def bar(foo = []) which doesn't do what you expect.

Answer 2

The first method offers you the opportunity to give your required argument a meaningful name; using *args doesn't. Using *args is great when you need it, but why give up the opportunity for clearer expression of your intent?

Answer 3

If you don't want arbitrary keyword arguments, leave out the ** parameter. For the love of all that is holy, if you have something that is required, just make it a normal argument.

Instead of this:

def test_method(*args, **kwargs):
    required_arg = kwargs.pop('required_arg')
    if kwargs:
        raise ValueError('Unexpected keyword arguments: %s' % kwargs)

Do this:

def test_method(required_arg, *args):
    pass