Iterators & Generators Highlights Summary

Every highlight bullet from the 11 pages in this section, gathered on one page and grouped by the page it came from.

Closures, Protocols & Lazy Evaluation

• for, with, and @decorator are syntax sugar over dunder-method protocols, not built-in special cases
• A generator function returns an object immediately; its body only runs incrementally, on demand
• Closures capture variables by reference to a shared cell, not by copying a value
• itertools and functools are composable building blocks over these same two ideas, not a separate system

Iterators & the Iterator Protocol

• Iterable has iter; iterator has next
• for loops call iter() then next() until StopIteration
• Generators are the easiest custom iterators
• collections.abc documents iteration interfaces

Generators & yield

• yield pauses function preserving local state
• Generators are single-pass iterators
• send/throw advanced but rarely needed
• Pipeline stages without intermediate lists

yield from & Sub-generators

• yield from delegates to sub-iterator
• Forwards send/throw/close to sub-generator
• Flattens nested iteration cleanly
• Replaces manual for/yield loops

itertools

• itertools returns lazy iterators
• groupby requires sorted input by key
• islice slices iterators without indexing
• product replaces nested for loops

functools

• lru_cache memoizes pure function calls
• partial binds arguments early
• wraps preserves decorator metadata
• singledispatch for type-based overloads

Closures & Scope Capture

• Nested functions close over enclosing variables
• Late binding trap in loops creating lambdas
• nonlocal rebinds enclosing names
• Closures power decorators and factories

Writing Decorators

• Decorators are callables wrapping callables
• @decorator syntax applies at import time
• wraps copies name and doc
• Parametrized decorators need factory function

Class & Method Decorators

• Class decorators mutate or wrap class objects
• Method decoration order matters with descriptors
• dataclass is a class decorator
• Register plugins by decorating classes

Context Managers

• with guarantees cleanup via exit
• contextmanager decorator builds managers from generators
• ExitStack composes many managers dynamically
• exit receives exception info

Iterators & Decorators Best Practices

• Prefer generators for large or streaming data
• Always use functools.wraps on decorators
• itertools over hand-rolled iterator loops
• Context managers for resource cleanup

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