03·itertools — Lazy Iterations

Introduction

itertools provides functions that generate lazy iterators — efficient, composable tools for working with sequences. Joining (chain), infinite (count, cycle, repeat), slicing and filtering (islice, takewhile, dropwhile, compress, filterfalse), combinatorics (product, permutations, combinations), aggregation (accumulate), grouping (groupby), mapping (starmap), zipping (zip_longest, tee). Lazy = no allocation of the full collection in memory.