Context Manager

what is context

the state surrounding a section of code

why we need a context manager

• writing try/finally every time can get cumbersom
• easy to forget closing the file

use cases

Useful for program that needs Enter / Exit handeling

• create / releasing resources
• database transaction
• set and reset decimal context

Common patterns

• open / close
• lock / release
• change / reset
• start / stop
• enter / exit

protocal

implement these two dunder methods:

• __enter__

  perform the setup, optionally return an object

• __exit__

  receives error (silence or propagate)

  • need arguments exc_type, exc_value, exc_trace to handle exception
  • return True to silence exception

  perform clean up

examples

contextlib

nested contexts