test_function_arbitrary_arguments.py

"""Arbitrary Argument Lists

@see: https://docs.python.org/3/tutorial/controlflow.html#arbitrary-argument-lists

Function can be called with an arbitrary number of arguments. These arguments will be wrapped up in
a tuple. Before the variable number of arguments, zero or more normal arguments may occur.
"""


def test_function_arbitrary_arguments():
    """Arbitrary Argument Lists"""

    # When a final formal parameter of the form **name is present, it receives a dictionary
    # containing all keyword arguments except for those corresponding to a formal parameter.
    # This may be combined with a formal parameter of the form *name which receives a tuple
    # containing the positional arguments beyond the formal parameter list.
    # (*name must occur before **name.) For example, if we define a function like this:
    def test_function(first_param, *arguments):
        """This function accepts its arguments through "arguments" tuple"""
        assert first_param == 'first param'
        assert arguments == ('second param', 'third param')

    test_function('first param', 'second param', 'third param')

    # Normally, these variadic arguments will be last in the list of formal parameters, because
    # they scoop up all remaining input arguments that are passed to the function. Any formal
    # parameters which occur after the *args parameter are ‘keyword-only’ arguments, meaning that
    # they can only be used as keywords rather than positional arguments.
    def concat(*args, sep='/'):
        return sep.join(args)

    assert concat('earth', 'mars', 'venus') == 'earth/mars/venus'
    assert concat('earth', 'mars', 'venus', sep='.') == 'earth.mars.venus'