Python function that takes one compulsory argument from two choices

Question

I have a function:

def delete(title=None, pageid=None):
    # Deletes the page given, either by its title or ID
    ...
    pass

However, m

Answer 1

If both arguments can have any value, including None, then the solution is to use a sentinel object for them. Then you can calculate a sum over the number of arguments that are set to non-default value:

NOT_SET = object()
def delete(title=NOT_SET, pageid=NOT_SET):
    if sum(i is not NOT_SET for i in [title, page_id]) != 1:
        raise ValueError('Can set only one of these')

This pattern is easily expandable to more arguments as well.