itertools module


Martin McBride, 2021-10-10
Tags itertools python standard library
Categories python standard library

The itertools module provides a set of functions that create iterators.

Some of these functions work in similar ways to the built-in functions on iterables, in particular the transforming and reducing functions. You may want to read that article of you are not familiar with map, filter, zip and sum.

This article covers all the functions in the itertools module, with examples. The functions are divided into groups that cover similar functionality:

  • General iterators - mainly variants on the built-in functions
    • Map-like iterators - starmap.
    • Filter-like iterators - filterfalse, dropwhile, takewhile, compress, and isslice.
    • Zip-like iterators - chain, chain.from_iterable, and zip_longest.
    • Splitting iterators - tee and groupby.
    • Accumulating iterators - accumulate.
  • Infinite iterators - count, cycle, and repeat.
  • Combinatoric iterators - product, permutations, combinations and combinations_with_replacement.

All these functions are contained in the itertools module, so you always import this module to use the functions. We haven't shown this in the examples, to avoid repetition, but you should include the import at the top of every example if you want to run them.

If you found this article useful, you might be interested in the book Python Quick Start or other books by the same author.

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