How Can I Pad Python\'s Zip Function to the Length of the Longest Iterable?

Extending Zip to Pad to Maximum Length

Zip is a built-in function in Python that combines multiple iterables. However, it stops at the length of the shortest iterable. What if we want to pad the results to match the length of the longest iterable?

Solution

In Python 3, itertools.zip_longest provides this functionality. It evaluates all iterables and pads with None by default, maintaining the alignment.

a = ['a1']
b = ['b1', 'b2', 'b3']
c = ['c1', 'c2']

list(itertools.zip_longest(a, b, c))

# [('a1', 'b1', 'c1'), (None, 'b2', 'c2'), (None, 'b3', None)]

You can customize the padding value using the fillvalue parameter:

list(itertools.zip_longest(a, b, c, fillvalue='foo'))

# [('a1', 'b1', 'c1'), ('foo', 'b2', 'c2'), ('foo', 'b3', 'foo')]

For Python 2, you can use itertools.izip_longest (Python 2.6 ) or map with None:

a = ['a1']
b = ['b1', 'b2', 'b3']
c = ['c1', 'c2']

map(None, a, b, c)

# [('a1', 'b1', 'c1'), (None, 'b2', 'c2'), (None, 'b3', None)]

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