Is there a zip-like function that pads to longest length in Python?
Is there a built-in function that works like zip() but that will pad the results so that the length of the resultant list is the length of the longest input rather than the shortest input?
>>> a = ['a1']
>>> b = ['b1', 'b2', 'b3']
>>> c = ['c1', 'c2']
>>> zip(a, b, c)
[('a1', 'b1', 'c1')]
>>> What command goes here?
[('a1', 'b1', 'c1'), (None, 'b2', 'c2'), (None, 'b3', None)]
Answer
In Python 3 you can use itertools.zip_longest
>>> list(itertools.zip_longest(a, b, c))
[('a1', 'b1', 'c1'), (None, 'b2', 'c2'), (None, 'b3', None)]
You can pad with a different value than None by using the fillvalue parameter:
>>> list(itertools.zip_longest(a, b, c, fillvalue='foo'))
[('a1', 'b1', 'c1'), ('foo', 'b2', 'c2'), ('foo', 'b3', 'foo')]
With Python 2 you can either use itertools.izip_longest (Python 2.6+), or you can use map with None. It is a little known feature of map (but map changed in Python 3.x, so this only works in Python 2.x).
>>> map(None, a, b, c)
[('a1', 'b1', 'c1'), (None, 'b2', 'c2'), (None, 'b3', None)]