Context Managers (with)

with thing as x: guarantees that setup runs first and cleanup runs after — even if the block raises.

Classic uses

• File I/O: with open(path) as f:
• Locks, DB transactions, temporary directories
• Timing, profiling, logging blocks

Build your own

@contextmanager on a generator function: code before yield is enter, code after yield is exit.

Try it

1. Write a silenced() context manager that swallows specific exceptions in its block.
2. Use timing to compare sum(range(N)) vs a manual for-loop sum.