with_previous

Python Morsels Exercise

Looping helper to get each iterable item along with the previous item

3 bonuses 7 hints 10 solutions 212 users solved 18 reviews

I want you to write a function that accepts a sequence (a list for example) and returns a new iterable (anything you can loop over) that includes a tuple of each item and the previous item (the item just before it). The first "previous item" should be None.

For example:

>>> list(with_previous("hello"))
[('h', None), ('e', 'h'), ('l', 'e'), ('l', 'l'), ('o', 'l')]
>>> list(with_previous([1, 2, 3]))
[(1, None), (2, 1), (3, 2)]

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