Safe and unsafe Python function calling patterns

calling_patterns.py

"""
A demonstration of safe and unsafe ways to write and call Python functions that
take required and optional arguments that are likely to change over time.

Try performing common refactoring operations on the functions such
as adding/removing required/optional args and changing args to and from
required to optional. Also consider combinations of these operations.

The calling patterns marked dangerous are likely to break in some of these
situations, whereas the safe pattern of always calling with keywords
is robust against errors and will immediately produce an exception when a
calling error is made.
"""


def fun1(a, b, c):
    return ' '.join([a, b, c])


def call_fun1_safe():
    print fun1(
        c = 'dogfood',
        b = 'eat',
        a = 'dog',
    )


def call_fun1_dangerous():
    print fun1('dog', 'eat', 'dogfood')


def fun2(a, b, c, d='', e=''):
    non_empty = [x for x in [a, b, e, c, d] if x]
    return ' '.join(non_empty)


def call_fun2_safe():
    print fun2(
        c = 'dogfood',
        b = 'eat',
        a = 'dog',
    )


def call_fun2_still_safe():
    print fun2(
        e = 'too much',
        d = 'then sleep',
        c = 'dogfood',
        b = 'eat',
        a = 'dog',
    )


def call_fun2_dangerous():
    print fun2('dog', 'eat', 'dogfood', 'then sleep', 'too much')


def call_fun2_still_dangerous():
    print fun2('dog', 'eat', 'dogfood', d='then sleep', e='too much')


if __name__ == '__main__':
    call_fun1_safe()
    call_fun1_dangerous()

    call_fun2_safe()
    call_fun2_dangerous()
    call_fun2_still_dangerous()