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Python: Iterable unpacking

Iterable unpacking allows to assign the elements of an iterable to multiple variables.

This technique is often used for «shift» like operations (as is for example known from the Perl function shift.

>>> print(  [1,2,3] )
[1, 2, 3]

>>> print( *[1,2,3] )
1 2 3

>>> [ (x, 'added') for x in [(1,2), (3,4), (5,6)]]
[((1, 2), 'added'), ((3, 4), 'added'), ((5, 6), 'added')]

>>> [ (*x, 'added') for x in [(1,2), (3,4), (5,6)]]
[(1, 2, 'added'), (3, 4, 'added'), (5, 6, 'added')]

Unpacking in a for … in loop

Iterable unpacking can also be applied in a for … in loop:

for foo, *bar, baz in [
      ( 'one', 'two', 'three', 'four', 'five' ),
      [    1 ,    2 ,      3 ,             5  ],
    ]:

    print(foo)
    print(bar)
    print(baz)
    print()

Github repository about-Python, path: /iterable/unpacking/for-in.py

This example prints:

one
['two', 'three', 'four']
five

1
[2, 3]
5

Packing

foo, *bar, baz = ( 'one', 'two', 'three', 'four', 'five' )

print(foo) #   one
print(bar) # ['two', 'three', 'four']
print(baz) #   five

Github repository about-Python, path: /iterable/unpacking/assignment.py

Type of an unpacked iterarable

The type of the portion of the iterable that was assigned to the variable with the * is list:

a, *b = (1, 2), 'a', 'b', 'c'

print(type(a))
#
#  <class 'tuple'>

print(type(b))
#
#  <class 'list'>

Github repository about-Python, path: /iterable/unpacking/type.py

Python: Iterable unpacking

Unpacking in a for … in loop

Packing

Type of an unpacked iterarable

See also