Interleave multiple lists of the same length in Python

Question

In Python, is there a good way to interleave two lists of the same length?

Say I\'m given [1,2,3] and [10,20,30]. I\'d like to transform th

Answer 1

Given

a = [1, 2, 3]
b = [10, 20, 30]
c = [100, 200, 300, 999]

Code

Assuming lists of equal length, you can get an interleaved list with itertools.chain and zip:

import itertools


list(itertools.chain(*zip(a, b)))
# [1, 10, 2, 20, 3, 30]

---

Alternatives

itertools.zip_longest

More generally with unequal lists, use zip_longest (recommended):

[x for x in itertools.chain(*itertools.zip_longest(a, c)) if x is not None]
# [1, 100, 2, 200, 3, 300, 999]

Many lists can safely be interleaved:

[x for x in itertools.chain(*itertools.zip_longest(a, b, c)) if x is not None]
# [1, 10, 100, 2, 20, 200, 3, 30, 300, 999]

more_itertools⁺

A library that ships with the roundrobin itertools recipe, interleave and interleave_longest.

import more_itertools


list(more_itertools.roundrobin(a, b))
# [1, 10, 2, 20, 3, 30]

list(more_itertools.interleave(a, b))
# [1, 10, 2, 20, 3, 30]

list(more_itertools.interleave_longest(a, c))
# [1, 100, 2, 200, 3, 300, 999]

yield from

Finally, for something interesting in Python 3 (though not recommended):

list(filter(None, ((yield from x) for x in zip(a, b))))
# [1, 10, 2, 20, 3, 30]

list([(yield from x) for x in zip(a, b)])
# [1, 10, 2, 20, 3, 30]

_{⁺Install using pip install more_itertools}