all Python 3contextlibterm

contextlib.contextmanager

decorator

Decorator that turns a generator function with a yield into a context manager.

Syntax

@contextlib.contextmanager
def my_cm(): ...; yield value; ...

If the with block raises, the exception is thrown back in at the yield point, so anything after yield is simply skipped. That is why cleanup almost always belongs in a try/finally around the yield — otherwise the resource leaks on errors. The object you get is single-use: the generator is exhausted after one with, so call the function again for a second block.

Examples

from contextlib import contextmanager
@contextmanager
def greet(name):
    print('enter')
    yield f'hi {name}'
    print('exit')
with greet('Bob') as msg:
    print(msg)  # → enter / hi Bob / exit

# Очистка — в finally: выполнится и при исключении внутри with
import os, tempfile
from contextlib import contextmanager
@contextmanager
def tmp_file(name):
    path = os.path.join(tempfile.gettempdir(), name)
    open(path, 'w').close()
    try:
        yield path
    finally:
        os.remove(path)
with tmp_file('demo.txt') as p:
    print(os.path.exists(p))  # → True
print(os.path.exists(p))  # → False

See also

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