[issue38941] xml.etree.ElementTree.Element inconsistent warning for bool

[Serhiy Storchaka]

Serhiy Storchaka <storchaka+cpython at gmail.com> added the comment:

Stefan's arguments looked reasonable to me. I supported deprecating Element.__bool__. This was an old plan, although we failed with deprecation in the C implementation (this is not the first oversight in deprecations in ElementTree).

But there is a problem: removing __bool__ will not change the value of bool(element). It will still return False for an Element without children, because bool() falls back to __len__ if __bool__ is not defined, and Element.__len__ is defined. So we will need either to define Element.__bool__ always returning True, and this will be the first case when __bool__ and __len__ return inconsistent values, or to deprecate __len__ (and perhaps __getitem__) that goes too far from the initial plan.

So now I am not sure. Making Element.__bool__ always returning True or raising an exception could help to fix some bugs in user code. But this differs from common behavior of sequence-like types in Python. On other hand, we have a precedence: bool(NotImplemented) raises an exception now (this also can save from common errors).

When I started to write this message I was -0 for changing Element.__bool__. Now I am +0, after considering all arguments that came in my mind, but still have doubts. Can we ask some of the language ideologues?

----------
nosy: +gvanrossum

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38941>
_______________________________________