Python context managers for resource cleanup

Resources like files, database connections, locks, and network sockets are not being properly closed, leading to resource leaks, locked files, or exhausted connection pools.

Always use context managers (with statement) for resources that need cleanup. (1) Files: with open('file.txt') as f: — auto-closes even if exception occurs. (2) Custom context manager with contextlib: @contextmanager def managed_resource(): resource = acquire(); try: yield resource; finally: release(resource). (3) Database: with conn.cursor() as cur: — auto-commits/rollbacks. (4) For multiple resources: with open('a') as f1, open('b') as f2:. (5) Async: async with aiohttp.ClientSession() as session:. (6) Never use try/finally for resource cleanup when a context manager is available.

Context managers guarantee cleanup via __exit__ even when exceptions occur. Manual try/finally is error-prone — developers forget to add it, or add it but miss edge cases.