The recipes hidden in the itertools documentation

Mon, 13 Jul 2026 00:00:00 +0000

At the end of the itertools page there is a section called Itertools Recipes: a collection of useful functions built by combining the module’s building blocks. Flattening a list of lists, finding the first element that passes a test, walking a sequence in windows: a lot of what you would write by hand is already solved there. The recipes do not come ready to use in itertools, the idea is to copy them into your code. We have already used one of them here, consume, in the article about consuming iterables without allocating memory. I picked three others that are worth knowing.

Consuming iterables without allocating memory

Wed, 17 Jun 2026 00:00:00 +0000

The problem Link to heading

When you just want to “run” a map/generator pipeline for its side effects (writing each item to a stream, for example), the reflex is a for or a list(...). The list allocates an entire list that gets thrown away right after, wasting memory for nothing. The for solves the memory issue, but the loop runs in pure Python.

The tip Link to heading

collections.deque accepts a maxlen parameter. With maxlen=0, it pulls each element and discards it immediately, never growing: that is the itertools consume recipe. Instead of materializing a list only to throw it away, you drain the pipeline in constant memory.

Iterators on cassiobotaro

The recipes hidden in the itertools documentation

Consuming iterables without allocating memory

The problem Link to heading

The tip Link to heading