Keyword-only arguments

Python 3 allows you to make some function arguments keyword-only, meaning they must be passed as (arg=value) rather than just (value).

It may be useful to prevent function calls like this: grep(text, pattern, True, False, True), where True, False, True actually means ignore case, don't invert match, pattern is Perl regexp. It would be nice to force the only reasonable form of this call:

grep(text, pattern,
    ignore_case=True,
    perl_regexp=True)

To achieve this result you should place the keyword-only arguments after varargs argument (aka *args):

def grep(
    text, pattern, *args,
    ignore_case=False,
    invert_match=False,
    perl_regexp=False,
):
    pass

If you don't need *args (like in the example), just replace it with a bare asterisk:

def grep(
    text, pattern, *,
    ignore_case=False,
    invert_match=False,
    perl_regexp=False,
):
    pass