Function Argument Unpacking

Putting a * operator before a tuple, list or generator, in a function call will unpack it and pass its elements as separate positional arguments to the called function.

def print_coordinate(x, y):
    print(x, y)

# tuple
coordinate = (1, 2)
print(*coordinate)

# list
coordinate = [3, 4]
print(*coordinate)

# generator
coordinate = (x for x in range(5, 7))
print(*coordinate)

# outputs:

1 2
3 4
5 6

Similarly, the ** operator will unpack keyword arguments from dictionaries and pass them to the called function.

def print_coordinate(x, y):
    print(x, y)

coordinate = {'x': 7, 'y': 8}
print_coordinate(**coordinate)

# outputs:

7 8

Another example:

def print_team(name, captain, rank):
    print(f'{name}, captained by {captain}, is ranked number {rank}')

# tuple
australia = ('Australia', 'Ponting', 1)
print_team(*australia)

# list
australia = ['Australia', 'Ponting', 2]
print_team(*australia)

# generator
australia = (x for x in ['Australia', 'Ponting', 3])
print_team(*australia)

# dictionary
australia = {'name': 'Australia', 'captain': 'Ponting', 'rank': 4}
print_team(**australia)

# outputs:

Australia, captained by Ponting, is ranked number 1
Australia, captained by Ponting, is ranked number 2
Australia, captained by Ponting, is ranked number 3
Australia, captained by Ponting, is ranked number 4

You may need to unpack specific values from an iterable, again the * operator is very useful. Here we grab the first and last name, and assign any other names to other – from the list middle:

def greet_new_member(fullname):
    first, *middle, last = fullname.split(' ')
    other = " ".join(middle)
    print(f'Member: {last}, {first} ({other})')
    print(f'Welcome {first}')

greet_new_member("Rainen Anthony Yi Hao Harper")

# outputs:

Member: Harper, Rainen (Anthony Yi Hao)
Welcome Rainen

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