Zip is its own inverse

You can undo the zipping operation using zip itself. Let’s explore that in Python. By using the unpacking operator * you don’t have to manually specify the number of arguments (although I do assume the return of two components in the example below). In Python 3, the zip operator returns a generator instead of a list, so you need to explicitly cast to a list if you want one.

>>> a = [1, 3]
>>> b = [2, 4]
>>> c = list(zip(a,b))
>>> c
[(1, 2), (3, 4)]
>>> a, b = list(zip(*c))
>>> a
(1, 3)
>>> b
(2, 4)

The inverse operation will always return tuples in Python, so if your original input was a list, you also need to convert back the results to a list.

This operation is super handy. For example, I wrote a class to recommend relevant texts for a query document based on their distance in a vector space. The recommend() function of this class returns a list of recommended texts and a list of tuples containing relevant metadata about those texts. So the metadata will be a list of (distance, document_id, type) tuples. We may be interested in easily retrieving all distances, document_ids etc. as a list of their own. We can do that by using the unpack+zip trick:

distances, document_ids, types = zip(*meta)