with Statement

The with statement is a cleaner alternative to try/finally for closing files and releasing locks. This chapter goes under the hood: how Python actually desugars a with statement, the exact order managers are entered and exited, what happens when __exit__ itself blows up, and the difference between reusable, reentrant, and one-shot managers. By the end, the surprises you might hit (a name still bound after the block, an exception that gets replaced, a half-set-up resource that still cleans up) will all make sense.