loop-better-trey-hunner.md

"Loop Better" by Trey Hunner

Anything that can be subject to a for loop is an iterable, and anything that is iterable can be subjected to a for loop Sequences are iterables that can be indexed numerically (lists, strings, etc.)

for loops

Q: How can we loop over an iterable without using a for loop? A1: You can use a while loop for sequences, but not for iterables in general A2: Wrap iterables in an iterator (iter) and progress the iterator (next())

>>> iterator = iter([1, 2, 3, 4, 5])
>>> iterator
<list_iterator object a 0x7ab35>
>>> next(iterator)
1

Notes about iterators

Iterators are unidirectional and get "used up" when you go through them Iterators are iterables and are their own iterators Iterators enable lazy evaluation; an item isn't evaluated until it's been iterated to Iterators allow for infinitely long iterables (look at itertools.count) You can produce generator-like behavior using the iterator protocol along with yield