Let’s Reiterate

In this chapter, you learned the following:

• Generator expressions yield items lazily (on demand), which saves memory for large datasets; pass them directly to aggregators like sum rather than materializing intermediate lists.

• Python offers iterator-centric helpers beyond basic loops. Most itertools functions and reversed return iterators you can feed into for loops, comprehensions, or other consumers, while sorted returns a list.

• Built-ins like enumerate and zip are iterators that pair indexes with values or walk multiple sequences in lockstep, handy for labeled iteration and managing parallel lists.

• Lambda functions passed to map and filter are useful for quick predicate checks (for example, “starts with #”) and simple transformations (for example, “strip the first char”).

• You can prototype simple text “summaries” by chaining itertools tools: tokenize, make word-pairs with combinations, flatten with chain.from_iterable, count with Counter.most_common, and keep frequent pairs with takewhile.

• For ordering, reversed just flips the existing order, while sorted actually orders by value. Python won’t sort heterogeneous types unless you supply a key function.

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