![]() Loop Better, the talk this article is based on.Loop Like a Native, Ned Batchelder's P圜on 2013 talk.Here are related articles and videos I recommend: PYTHON FOR LOOP GENERATORIf you'd like to make a lazy iterable in your code, think of iterators and consider making a generator function or a generator expression.Īnd finally, remember that every type of iteration in Python relies on the iterator protocol, so understanding the iterator protocol is the key to understanding quite a bit about looping in Python in general. Iterators are the most rudimentary form of iterables in Python. When someone says the word "iterable," you can only assume they mean "something that you can iterate over." Don't assume iterables can be looped over twice, asked for their length, or indexed. Sequences are iterables, but not all iterables are sequences. Both use the iterator protocol, so you get the same result in both cases. Unpacking a dictionary is really the same as looping over the dictionary. Iterable unpacking also relies on the iterator protocol. For example Python's enumerate and reversed objects are iterators. Many of Python's built-in classes are iterators also. I've already mentioned that generators are iterators. You've already seen lots of iterators in Python. And we can create iterables that are conservative with system resources, can save us memory, and can save us CPU time. Because we can create lazy iterables, we can make infinitely long iterables. Iterators allow us to both work with and create lazy iterables that don't do any work until we ask them for their next item. Anything that returns itself when passed to iter is an iterator.Anything that can be passed to next without a TypeError is an iterator.Anything that can be passed to iter without a TypeError is an iterable.The inverse of these statements also holds true: Can be passed to the iter function and will return themselves back.Can be passed to the next function, which will give their next item or raise a StopIteration exception if there are no more items.Iterables can be passed to the iter function to get an iterator for them. Let's define how iterators work from Python's perspective. You can think of iterators as lazy iterables that are single-use, meaning they can be looped over one time only.Īs you can see in the truth table below, iterables are not always iterators but iterators are always iterables: Object ![]()
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