Using args when calling functions

The effect of using the * operator on an argument when calling a function is that of unpacking the list or a tuple argument

def print_args(arg1, arg2):
    print(str(arg1) + str(arg2))

a = [1,2]
b = tuple([3,4])

print_args(*a)
# 12
print_args(*b)
# 34

Note that the length of the starred argument need to be equal to the number of the function’s arguments.

A common python idiom is to use the unpacking operator * with the zip function to reverse its effects:

a = [1,3,5,7,9]
b = [2,4,6,8,10]

zipped = zip(a,b)
# [(1,2), (3,4), (5,6), (7,8), (9,10)]

zip(*zipped)
# (1,3,5,7,9), (2,4,6,8,10)