Unpacking

Unpacking is the process of getting out stuff — iterables such as lists, tuples, and dictionaries. We use the asterisks (*, **) before an iterable to unpack it.

The asterisk operator (*) is used to unpack all the values of an iterable that have not been assigned yet.

>>> first, *unused, last = [1, 2, 3, 5, 7]
>>> first
1
>>> last
7
>>> unused
[2, 3, 5]

>>> first, *_, last = [1, 2]
>>> first
1
>>> last
2
>>> _
[]

>>> *string, = 'PythonIsTheBest'
>>> string
['P', 'y', 't', 'h', 'o', 'n', 'I', 's', 'T', 'h', 'e', 'B', 'e', 's', 't']

>>> *numbers, = range(5)
>>> numbers
[0, 1, 2, 3, 4]

While a single asterisk is used to unpack lists and tuples, the double-asterisk (**) is used to unpack dictionaries.

>>> food = {'fish':3, 'meat':5, 'pasta':9} 
>>> colors = {'red': 'intensity', 'yellow':'happiness'}
>>> merged_dict = {**food, **colors}
>>> merged_dict
{'fish': 3, 'meat': 5, 'pasta': 9, 'red': 'intensity', 'yellow': 'happiness'}

Packing with the * operator (args)

>>> def product(n1, n2):
...     return n1 * n2
... 
>>> numbers = [12, 1]
>>> product(*numbers)
12

>>> def test_type(*args):
...     print(type(args))
...     print(args)
... 
>>> test_type(1, 2, 4, 'a string')
<class 'tuple'>
(1, 2, 4, 'a string')

Packing with the ** operator (kwargs)

The ** operator is used exclusively for dictionaries. This means that with this operator we’re able to pass key-value pairs to the function as a parameter.

>>> def make_person(name, **kwargs):
...     result = name + ': '
...     for key, value in kwargs.items():
...             result += f'{key} = {value}, '
...     return result
... 
>>> make_person('Melissa', id=12112, location='london', net_worth=12000)
'Melissa: id = 12112, location = london, net_worth = 12000, '

>>> def test_kwargs(**kwargs):
...     print(type(kwargs))
...     print(kwargs)
... 
>>> test_kwargs(random=12, parameters=21)
<class 'dict'>
{'random': 12, 'parameters': 21}

Note: kwargs is just a convention you can name this parameter with whatever you want

>>> def my_final_function(*args, **kwargs):
...     print('Type args: ', type(args))
...     print('args: ', args)
...     print('Type kwargs: ', type(kwargs))
...     print('kwargs: ', kwargs)
... 
>>> my_final_function('Python', 'The', 'Best', language='Python', users='A lot')
Type args:  <class 'tuple'>
args:  ('Python', 'The', 'Best')
Type kwargs:  <class 'dict'>
kwargs:  {'language': 'Python', 'users': 'A lot'}