What is the difference between except Exception and a bare except:? Why is the bare form discouraged?
except Exception catches application errors; bare except catches everything including SystemExit and KeyboardInterrupt
In Python 3, every exception derives from BaseException. SystemExit, KeyboardInterrupt, and GeneratorExit are direct subclasses of BaseException, not Exception. except Exception catches only the Exception subtree, so Ctrl+C and sys.exit() still work as expected. A bare except: is equivalent to except BaseException: and will swallow KeyboardInterrupt, SystemExit, and GeneratorExit, which breaks shutdown signals and makes a process unkillable with Ctrl+C. That is the actual reason it is discouraged: it is not about style, it is about keeping the control-flow exceptions that are not application errors out of your handler.
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BaseException: SystemExit, KeyboardInterrupt, GeneratorExit, and Exception.
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Exception: the branch for ordinary application and library errors. This is what you almost always want.
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Catch the narrowest exception you can handle. Catching something you cannot recover from just hides the failure.
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Use bare except only in rare cleanup code that must run for any exit reason, and immediately re-raise with raise.
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Common mistake: writing except: pass during debugging, which swallows the error and makes root cause invisible.
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Common mistake: assuming except Exception catches everything. It does not catch KeyboardInterrupt or SystemExit.
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Version note: Python 2 allowed raising old-style strings and had a different hierarchy in some edge cases; the modern hierarchy described here is Python 3.
Scenario Questions
0-2 years experience
- 1Why does Ctrl+C stop working after someone added a bare except around a loop?
- 2Which base class should you almost always catch?
2-5 years experience
- 1A service hangs instead of shutting down on SIGTERM. How do you find the bare except that is swallowing SystemExit?
- 2You need to log every error but never mask Ctrl+C. How do you structure the handler?
5-8 years experience
- 1You are reviewing a codebase with dozens of bare excepts. How do you prioritize which to fix and what replacement patterns do you apply?
- 2You maintain a library and your users complain that KeyboardInterrupt is swallowed by one of your functions. How do you fix it without breaking callers?
8+ years experience
- 1Design a top-level error boundary for a long-running service that catches application errors, logs them, and still honors shutdown signals and cancellation.
- 2Explain how BaseException interacts with async cancellation, GeneratorExit, and context managers, and how to write boundaries that do not break them.
Follow-up Questions
- What exceptions live outside the Exception subtree and why does that matter?
- When is it acceptable to write a bare except and what must you do inside it?