Description

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Advanced · 14 min

Context managers

Set up and clean up resources reliably with with.

Guarantee cleanup

A context manager runs entry and exit behavior around a with block, even when the block raises an exception.

class Session:
    def __enter__(self):
        print("Open")
        return self
    def __exit__(self, exc_type, exc, traceback):
        print("Close")

with Session():
    print("Use")

Output

Open
Use
Close

Create one with a generator

contextlib.contextmanager turns a generator with one yield into a context manager. Code after yield performs cleanup.

from contextlib import contextmanager

@contextmanager
def timer():
    print("Begin")
    yield
    print("End")

with timer():
    print("Run")

Output

Begin
Run
End

Context managers

  1. Read both context managers examples before answering.
  2. Run the task, compare its exact output, and revise the code if needed.

Try it yourself

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Manage a status

Complete active_status so it displays Active before the with block and Inactive after it. Keep the supplied block.

Practice