Python Academy · Lesson

contextlib: @contextmanager

Create context managers concisely with the contextlib decorator.

Lesson 3 of 413 steps

contextlib: @contextmanager is a free Python Academy lesson on CoddyKit. This is lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Python Academy learning path, and your progress syncs across the web and the CoddyKit app. The Python Academy course includes 4 lessons in total.

Why contextlib?

contextlib.contextmanager lets you write a context manager as a generator function instead of a class, reducing boilerplate.

from contextlib import contextmanager

@contextmanager
def managed():
    print("setup")
    yield
    print("teardown")

with managed():
    print("inside")

Yielding a Value

Whatever you yield is bound to the as variable in the with statement.

from contextlib import contextmanager

@contextmanager
def temp_list():
    lst = []
    yield lst
    print(f"Final list: {lst}")

with temp_list() as lst:
    lst.append(1)
    lst.append(2)

Exception Handling in @contextmanager

Wrap the yield in a try/finally to guarantee cleanup even if an exception occurs.

from contextlib import contextmanager

@contextmanager
def safe_open(path):
    f = open(path)
    try:
        yield f
    finally:
        f.close()

with safe_open("data.txt") as f:
    print(f.read())

Suppressing Exceptions

Catch the exception inside the generator to suppress it — same as returning True from __exit__.

from contextlib import contextmanager

@contextmanager
def ignore_value_errors():
    try:
        yield
    except ValueError:
        pass

with ignore_value_errors():
    raise ValueError("ignored")

contextlib.suppress

contextlib.suppress(*exceptions) is a ready-made context manager that suppresses specified exception types.

from contextlib import suppress

with suppress(FileNotFoundError):
    open("missing.txt")

print("continues")

contextlib.closing

closing(obj) creates a context manager that calls obj.close() on exit. Useful for objects that have close() but no __exit__.

from contextlib import closing
from urllib.request import urlopen

with closing(urlopen("https://example.com")) as page:
    content = page.read()

contextlib.nullcontext

nullcontext is a no-op context manager. Useful when a context manager is optional.

from contextlib import nullcontext

def process(data, lock=None):
    cm = lock if lock is not None else nullcontext()
    with cm:
        return [x*2 for x in data]

contextlib.ExitStack

ExitStack lets you manage a variable number of context managers dynamically.

from contextlib import ExitStack

files = ["a.txt", "b.txt", "c.txt"]
with ExitStack() as stack:
    handles = [stack.enter_context(open(f)) for f in files]
    data = [h.read() for h in handles]

Reusing a @contextmanager

A generator-based context manager is single-use per call. Call the decorated function again to reuse it.

from contextlib import contextmanager

@contextmanager
def counter():
    count = 0
    yield lambda: count.__add__  # each call is independent
    print("done")

with counter():
    pass
with counter():
    pass

asynccontextmanager

For async code, use contextlib.asynccontextmanager to write async with managers as generators.

from contextlib import asynccontextmanager

@asynccontextmanager
async def async_session():
    session = await create_session()
    try:
        yield session
    finally:
        await session.close()

contextlib.redirect_stdout

Redirect standard output to any file-like object temporarily.

import io
from contextlib import redirect_stdout

buf = io.StringIO()
with redirect_stdout(buf):
    print("captured")

print(buf.getvalue())  # captured

Quick Check

In a @contextmanager generator, where should cleanup code be placed to guarantee it runs even on exception?

Answer it in the interactive lesson

Recap

@contextmanager turns a generator into a context manager. Use try/finally around yield for safe cleanup. The contextlib module also provides suppress, nullcontext, ExitStack, and more.

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Frequently Asked Questions

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Yes — the full text of “contextlib: @contextmanager” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Python Academy course, upgrade to CoddyKit PRO. The Python Academy course includes 4 lessons in total.

What will I learn in “contextlib: @contextmanager”?

Create context managers concisely with the contextlib decorator. You practise Python Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

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No prior experience is required. Python Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

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