Recipes: Iterators and generators

Task-focused how-tos. If you know what you want to do but aren't sure how to build it, this is the section to skim.

Recipes in this section

• Process a large file lazily — streaming a file line by line (or record by record) without loading it all into memory. The pattern that lets you process multi-gigabyte inputs on a laptop.
• Chain and group iterables — itertools.chain for concatenation, groupby for runs of adjacent equal values, zip and zip_longest for parallel iteration.
• Combine generators into a pipeline — stacking filter → transform → window → aggregate as generators that feed each other. The functional-pipeline style for data processing.
• Avoid common iterator mistakes — a catalogue of the gotchas: once-consumed iterators, mutating during iteration, generator-inside-a-try, late binding in generator expressions.