Issue 33900: collections.counter update method without argument gives misleading error (original) (raw)

Issue33900

Created on 2018-06-19 07:54 by xtreak, last changed 2022-04-11 14:59 by admin. This issue is now closed.

Messages (3)
msg319935 - (view)	Author: Karthikeyan Singaravelan (xtreak) *	Date: 2018-06-19 07:54
There was a change made in collections.Counter that made it accept self as the first parameter and hence while doing *args in the method signature args[0] is always set as the self. Hence the check for `not args` becomes a no-op during collection_object.update() calls and the type error is not raised. This is only triggered when it's called as a class method like `Counter.update` and the error message is misleading "descriptor 'update' of 'Counter' object "needs an argument" which says update method of Counter object needs an argument though we are calling the method on class and also calling update on Counter object doesn't need an argument since counter_object.update() works fine as no-op. I think the error message could be improved since argument is not necessary for counter_object.update. Relevant commit : https://github.com/python/cpython/commit/ae5cb214d2cd41d96943a0ef43a4e95bd9a10b7a#diff-f30cb98704c3ccaf71deaf5503f7f4a1R587 No argument to counter object update test case : https://github.com/python/cpython/blob/ae5cb214d2cd41d96943a0ef43a4e95bd9a10b7a/Lib/test/test_collections.py#L1077 Calling update on Counter class test case : https://github.com/python/cpython/commit/20994f1e27c38973f1854dbdcf9b29fe8e3cd6be#diff-b5f669eab2fa576572b6115caa24427fR928 # Python 3 ➜ cpython git:(master) ✗ ./python Python 3.8.0a0 (heads/bpo33830-httplib-docs-fix-dirty:9bf0fb8, Jun 18 2018, 17:09:54) [GCC 5.4.0 20160609] on linux Type "help", "copyright", "credits" or "license" for more information. >>> from collections import Counter >>> c = Counter("Hello") >>> Counter.update() Traceback (most recent call last): File "", line 1, in File "/user/karthik/cpython/Lib/collections/__init__.py", line 638, in update raise TypeError("descriptor 'update' of 'Counter' object " TypeError: descriptor 'update' of 'Counter' object needs an argument >>> Counter.update(1) # No error since we check for the first argument to be iterable >>> c.update() # No args works fine though there was an above error with TypeError: descriptor 'update' of 'Counter' object needs an argument when called on class >>> Counter.update(1, foo=1) # 1 is considered as self here, a valid counter object works fine and is updated Traceback (most recent call last): File "", line 1, in File "/user/karthik/cpython/Lib/collections/__init__.py", line 655, in update self.update(kwds) AttributeError: 'int' object has no attribute 'update' Thanks
msg319939 - (view)	Author: Serhiy Storchaka (serhiy.storchaka) *	Date: 2018-06-19 08:38
This error is correct. It is the same as for dict.update. >>> dict.update() Traceback (most recent call last): File "", line 1, in TypeError: descriptor 'update' of 'dict' object needs an argument Perhaps you missed the difference between a descriptor and a method.
msg319940 - (view)	Author: Karthikeyan Singaravelan (xtreak) *	Date: 2018-06-19 08:46
Okay, got it. Sorry for the noise. Closing it. Thanks