Is the Context Managers (`with`) lesson free?

Yes. The first 5 lessons on PyRun are free forever — no signup, no card. Context Managers (`with`) runs real Python in your browser via Pyodide.

How long does the Context Managers (`with`) lesson take?

About 7 minutes end-to-end. It's a hands-on lesson — you read a paragraph, edit the code, and run it in the same tab.

Do I need to install Python to try the Context Managers (`with`) lesson?

No install required. PyRun runs real CPython in your browser via Pyodide (Python compiled to WebAssembly). Works on Chrome, Firefox, Safari, and Edge — desktop or mobile.

What level is the Context Managers (`with`) lesson?

Intermediate level. Best after finishing the Beginner track (syntax, control flow, functions, data types).

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Intermediate·7 min·intermediate · resources

Context Managers (`with`)

You’ll be able to

Use with statements to auto-manage resources
Understand what __enter__ and __exit__ do
Write your own context managers with contextlib
Guarantee cleanup even when errors occur

Why this matters

Every open(), requests.Session(), SQLAlchemy session.begin(), and threading.Lock is a context manager. Skipping with blocks is why production servers leak file handles and DB connections. contextlib.contextmanager and ExitStack are quiet superpowers.

Common pitfalls

Opening files without with — on CPython it works via refcount GC, but breaks on PyPy or under exceptions.
Forgetting to yield inside a @contextmanager function — the with block silently gets None.
Swallowing exceptions in __exit__ by returning truthy — only return True when you truly want to suppress.

with thing as x: guarantees that setup runs first and cleanup runs after — even if the block raises.

Classic uses

File I/O: with open(path) as f:
Locks, DB transactions, temporary directories
Timing, profiling, logging blocks

Build your own

@contextmanager on a generator function: code before yield is enter, code after yield is exit.

Try it

Write a silenced() context manager that swallows specific exceptions in its block.
Use timing to compare sum(range(N)) vs a manual for-loop sum.

Practice

3 graded exercises

Write the code, click Check. We’ll tell you exactly what to fix.

Progress0 / 3

Exercise 1
Use io.StringIO as a context manager to write two lines into it, then print the captured contents. Expected output includes both hello and world on separate lines.
Exercise 2
Use contextlib.contextmanager to write a timing(label) context manager that prints "<label>: done" on exit. Then use with timing("work"): around sum(range(100)). Expected output includes work: done.
Exercise 3
Write a context manager silenced(*exceptions) (as a class OR via @contextmanager) that swallows any of the given exception types inside its block. Test it with a divide-by-zero inside with silenced(ZeroDivisionError):, then print "after". Expected: after is printed and no error surfaces.

← PreviousErrors & try/except Next →Modules & Imports

Context Managers (`with`)

You’ll be able to

Use with statements to auto-manage resources
Understand what __enter__ and __exit__ do
Write your own context managers with contextlib
Guarantee cleanup even when errors occur

Why this matters

Common pitfalls

Opening files without with — on CPython it works via refcount GC, but breaks on PyPy or under exceptions.
Forgetting to yield inside a @contextmanager function — the with block silently gets None.
Swallowing exceptions in __exit__ by returning truthy — only return True when you truly want to suppress.

with thing as x: guarantees that setup runs first and cleanup runs after — even if the block raises.

Classic uses

File I/O: with open(path) as f:
Locks, DB transactions, temporary directories
Timing, profiling, logging blocks

Build your own

@contextmanager on a generator function: code before yield is enter, code after yield is exit.

Try it

Write a silenced() context manager that swallows specific exceptions in its block.
Use timing to compare sum(range(N)) vs a manual for-loop sum.

Practice

3 graded exercises

Write the code, click Check. We’ll tell you exactly what to fix.

Progress0 / 3

Exercise 1
Use io.StringIO as a context manager to write two lines into it, then print the captured contents. Expected output includes both hello and world on separate lines.
Exercise 2
Use contextlib.contextmanager to write a timing(label) context manager that prints "<label>: done" on exit. Then use with timing("work"): around sum(range(100)). Expected output includes work: done.
Exercise 3
Write a context manager silenced(*exceptions) (as a class OR via @contextmanager) that swallows any of the given exception types inside its block. Test it with a divide-by-zero inside with silenced(ZeroDivisionError):, then print "after". Expected: after is printed and no error surfaces.