Chapter 09 | The Context Management Protocol | Hooking into Python's with Statement

Context Management protocol

Python supports simple context management in the standard library (contextlib module)
The module dictates that, two magic methods should be present
- __enter__
  - The interpreter invokes the object's __enter__ method before the with statement's suite starts.
- __exit__
  - The interpreter always invokes the object's __exit__ method after the with statement suite ends.
If we create a class with the above two magic method we can safely say it conforms to the context management protocol.
We can also use __init__ magic method into the above combination.
- __init__ is executed even before __enter__.
- Defining __init__ is not mandatory in the context management protocol.

with open('todos.txt') as tasks:
    for chore in tasks:
        print(chore, end="")

__init__ is invoked as soon as the interpreter see the with statement.
__enter__ is invoked soon after the __init__ is invoked.
__exit__ is invoked at the end of the with statement.
- __exit__ take's few extra parameter to inform about wrong full termination of with statement.
Flask has an internal configuration called app.config which is a dictionary.