Issue 32464: raise NotImplemented vs return NotImplemented (original) (raw)

Issue32464

Created on 2017-12-31 11:44 by thatiparthy, last changed 2022-04-11 14:58 by admin. This issue is now closed.

Messages (3)
msg309277 - (view)	Author: Srinivas Reddy Thatiparthy(శ్రీనివాస్ రెడ్డి తాటిపర్తి) (thatiparthy) *	Date: 2017-12-31 11:44
I ran these queries on cpython repo. ➜ cpython git:(master) ✗ grep -r . -e return --include=\*.py | grep NotImplemented	wc -l 196 ➜ cpython git:(master) ✗ grep -r . -e raise --include=\*.py	grep NotImplemented	wc -l 295 I have always used raise NotImplemented or raise NotImplementedError. But when does it make sense to return NotImplemented?
msg309278 - (view)	Author: Mark Dickinson (mark.dickinson) *	Date: 2017-12-31 11:57
Here's the documentation, which I think explains all this clearly: briefly, `return NotImplemented` and `raise NotImplementedError` are the normal usages. `raise NotImplemented` doesn't make sense, and shouldn't be used: it'll end up raising a `TypeError`, sine `NotImplemented` is neither a subclass nor an instance of BaseException. NotImplemented: https://docs.python.org/3.7/library/constants.html#NotImplemented NotImplementedError: https://docs.python.org/3.7/library/exceptions.html#NotImplementedError Almost all of the grep results you're seeing do follow the expected patterns (either `return NotImplemented` or `raise NotImplementedError`, but a quick grep does show some questionable uses of `raise NotImplemented` in the standard library: MacBook-Pro:cpython mdickinson$ grep -r . -e raise --include=\*.py | grep "\bNotImplemented\b" ./Lib/asyncio/transports.py: The implementation here raises NotImplemented for every method ./Lib/idlelib/debugger_r.py: raise NotImplemented("dict_keys not public or pickleable") ./Lib/ssl.py: raise NotImplemented("Can't dup() %s instances" % The other way around also turns up an odd-looking `return NotImplementedError` (along with a false positive): MacBook-Pro:cpython mdickinson$ grep -r . -e return --include=\*.py	grep "\bNotImplementedError\b" ./Lib/ctypes/test/test_simplesubclasses.py: return NotImplementedError ./Lib/test/test_asyncio/test_transports.py: self.assertRaises(NotImplementedError, transport.get_returncode)
msg318070 - (view)	Author: Yury Selivanov (yselivanov) *	Date: 2018-05-29 19:11
Seems this issue isn't a bug and can be closed.