Call function without optional arguments if they are None

Question

There\'s a function which takes optional arguments.

def alpha(p1=\"foo\", p2=\"bar\"):
     print(\'{0},{1}\'.format(p1, p2))

Let me iterat

Answer 1

But assume that alpha is used in other places where it is actually supposed to handle None as it does.

To respond to this concern, I have been known to have a None-like value which isn't actually None for this exact purpose.

_novalue = object()

def alpha(p1=_novalue, p2=_novalue):
    if p1 is _novalue:
        p1 = "foo"
    if p2 is _novalue:
        p2 = "bar"
    print('{0},{1}'.format(p1, p2))

Now the arguments are still optional, so you can neglect to pass either of them. And the function handles None correctly. If you ever want to explicitly not pass an argument, you can pass _novalue.

>>> alpha(p1="FOO", p2=None)
FOO,None
>>> alpha(p1="FOO")
FOO,bar
>>> alpha(p1="FOO", p2=_novalue)
FOO,bar

and since _novalue is a special made-up value created for this express purpose, anyone who passes _novalue is certainly intending the "default argument" behavior, as opposed to someone who passes None who might intend that the value be interpreted as literal None.