Sequence unpacking

Extracting values and assigning them to variables. As list and tuple are ordered, they support unpacking. Unordered sequences like dictionaries don't support unpacking.

Example

# list
language = ['Python', 'PHP', 'NodeJS']
# unpacking
django, laravel, express = language
print(django, laravel, express)
# Python PHP Java

# tuple
color = (225, 110, 20)
red, green, blue = color
print(red, green, blue)
# 225 110 20

use * to unpack rest of the values

language = ['Python', 'PHP', 'NodeJS']
# unpacking with *
django, *others = language
print(django, others)
# Python ['PHP', 'NodeJS']

use _ to ignore values

language = ['Python', 'PHP', 'NodeJS']
# ignore values with _
django, _, express = language
print(django, express)
# Python NodeJS

use * to unpack list into positional arguments

When calling a function, you can unpack a list into positional arguments. List must have same length as number of positional arguments.

django = ['Python', 'MVT']

def create_django_app(language, architecture):
    return f'App created with {language} using {architecture} architecture'

# unpacking with * into positional arguments
print(create_django_app(*django))
# App created with Python using MVT architecture

use ** to unpack dictionary into keyword arguments

When calling a function, you can unpack a dictionary into keyword arguments. Dictionary keys name and element length must match function arguments.

django = {
    'language': 'Python',
    'architecture': 'MVT',
}

def create_django_app(language, architecture):
    return f'App created with {language} using {architecture} architecture'

# unpacking with ** into keyword arguments
print(create_django_app(**django))
# App created with Python using MVT architecture

use ** to copy keys from existing dictionary

When creating a new copy of a dictionary, you can copy keys from existing dictionary. Then you can override the values of the copied keys or even create new keys.

my_guitar = {
    'brand': 'Ibanez',
    'year': 2020,
}

# copy keys from existing dictionary, override value and create new key
my_new_guitar = {**my_guitar, 'year': 2021, 'color': 'Aqua'}

print(my_new_guitar)
# {'brand': 'Ibanez', 'year': 2021, 'color': 'Aqua'}

use ** to merge dictionaries

You can merge dictionaries using ** operator.

guitar_info ={
    'design': 'RG',
    'body': 'Poplar',
    'neck': 'Maple',
    'color': 'Aqua',
}

guitar_manufacturer = {
    'brand': 'Ibanez',
    'year': 2020,
}

# merge dictionaries
guitar = {**guitar_manufacturer, **guitar_info}

print(guitar)
# {'brand': 'Ibanez', 'year': 2020, 'design': 'RG', 'body': 'Poplar', 'neck': 'Maple', 'color': 'Aqua'}

You could also use | operator to merge dictionaries. python > 3.9

guitar = guitar_manufacturer | guitar_info