Unpacking function arguments

When you want to create a function that can accept any number of arguments, and not enforce the position or the name of the argument at “compile” time, it’s possible and here’s how:

def fun1(*args, **kwargs):
    print(args, kwargs)

The *args and **kwargs parameters are special parameters that are set to a tuple and a dict, respectively:

fun1(1,2,3)
# Prints: (1, 2, 3) {}
fun1(a=1, b=2, c=3)
# Prints: () {'a': 1, 'b': 2, 'c': 3}
fun1('x', 'y', 'z', a=1, b=2, c=3)
# Prints: ('x', 'y', 'z') {'a': 1, 'b': 2, 'c': 3}

If you look at enough Python code, you’ll quickly discover that it is widely being used when passing arguments over to another function. For example if you want to extend the string class:

class MyString(str):
    def __init__(self, *args, **kwarg):
        print('Constructing MyString')
        super(MyString, self).__init__(*args, **kwarg)