Context
Context managers simplify resource management by automatically setting up and tearing down resources. The `with` statement is Python's primary interface for context manager protocol. The guide walks through The with Statement, __enter__ & __exit__, contextlib.contextmanager, contextlib Utilities, Async Context Managers. `with expression as variable:` executes the context manager's `__enter__` method, assigns the result to `variable`, runs the block, and calls `__exit__` even if an exception occurs. This pattern is essential for files, locks, database connections, and other resources. `__enter__(self)` returns the resource to be assigned to the `as` target. `__exit__(self, exc_type, exc_val, exc_tb)` handles cleanup. Return `True` from `__exit__` to suppress exceptions. Parameters are `None` when no exception occurred. The `@contextmanager` decorator converts a generator function into a context manager. Code before `yield` runs in `__enter__`, the yielded value is the `as` target, and code after `yield` runs in `__exit__`. Wrap in `try/finally` for exception-safe cleanup. The guide is organized into 5 sections that build on each other, each pairing a prose explanation with runnable code.