Summary - Context managers

Combine @contextmanager and ExitStack to write a resource pool.

Summary - Context managers

In this group you learned five core concepts:

with — auto-closes a resource
__enter__/__exit__ — class-based context manager
@contextmanager — function-based context manager
exception catching — suppressing errors in __exit__
ExitStack — dynamic multi-management

Now you will do two short tasks that combine them: one with a class-based CM, one with @contextmanager.

Exercise Class-based context manager

Define class Log:. In __enter__ write print("aç") and return self. In __exit__ write print("kapat"). Inside a with Log(): block write print("çalışıyor").

Show example solution

class Log:
    def __enter__(self):
        print("aç")
        return self
    def __exit__(self, *a):
        print("kapat")

with Log():
    print("çalışıyor")

Exercise Block with @contextmanager

Write from contextlib import contextmanager. Define def blok(): with @contextmanager. In the body write print("başla"), yield, print("bitir"). Inside with blok(): write print("içeride").

Show example solution

from contextlib import contextmanager

@contextmanager
def blok():
    print("başla")
    yield
    print("bitir")

with blok():
    print("içeride")

Test yourself

Which is the shortest way to write a context manager?
- Class + __enter__/__exit__
- try/finally
- ExitStack
- @contextmanager + yield
Show answer

@contextmanager + yield — @contextmanager makes a CM from a function; no need to write a class.
Match context manager concepts

with

Starts the block
__enter__

Opening
__exit__

Closing
yield

Split in CM

Next lesson: Project design

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