Control Flow and Concurrency

This part is about the moments when Python’s control flow stops being plain if/for/while and starts being something else: an iterator’s __next__, a context manager’s __enter__/__exit__, a coroutine’s await, a thread’s Lock. Each one is a contract; this part is about what each contract promises.

• 28  Operator Overloading is the practical guide to making +, -, *, and == work on your own classes. The trick is the reflected methods — __radd__, __rmul__ — that let 2 * vec work even when vec doesn’t know about int.

• 29  Iterators, Generators, and Classic Coroutines is the engine room. Generators, yield from, lazy evaluation, the itertools module, and the duality between iterators and classic coroutines.

• 30  with, match, and else Blocks covers three pieces of Python control flow that don’t appear in many other languages: context managers (with), structural pattern matching (match), and the else clause on for/while/try.

• 31  Concurrency Models in Python is the conceptual chapter. Threads vs. processes vs. coroutines; the GIL; what it means for I/O-bound vs. CPU-bound work. Read it before the next two.

• 32  Concurrent Executors covers concurrent.futures — the high-level pool API that hides most of the locking and process management you’d otherwise write by hand.

• 33  Asynchronous Programming closes the part with asyncio itself: async def, await, the event loop, and the patterns (gather, semaphore, async for, async with) you reach for once you’re past Hello, World.