New submission from Emanuel Barry:
Attached patch changes bare attribute errors to add a useful error message. As
such, `raise AttributeError` and `raise AttributeError(None)` (but not `raise
AttributeError('')` for example) inside any of the attribute lookup or
descriptor methods (__getattribute__, __getattr__, __setattr__, __delattr__,
__get__, __set__, and __delete__). This is a followup to #27794.
As such, the following is now much more useful and less boilerplate:
class A:
_dynamic_names = {}
def __getattr__(self, name):
if name in self._dynamic_names:
return self._dynamic_names[name]
raise AttributeError
Then, doing the following:
A().spam
Will result in a `AttributeError("'A' object has no attribute 'spam'")`, while
keeping the original traceback. The patch is pretty much complete, but I have a
few concerns:
- Performance hit, especially on something that's used virtually everywhere and
everytime (attribute access); although PEP 487's __set_name__ lookup already
hurts performance slightly. The few micro-benchmarks I ran weren't very
significant, but there is a small drop in performance nonetheless.
- Four new PyErr_* API functions, one which isn't used in the current patch,
but since it's 3 lines I decided to leave it in anyway.
- I don't carry over the cause or context of the raised exception to the new
one. Keeping the traceback around is pretty trivial, since it has its own slot
in the thread state struct, but since not all exceptions are actual exceptions
at the C level (and the new exceptions I raise aren't either, at the C level),
I don't know how to carry over context or cause.
Oh, and exceptions set at the C level with e.g. `PyErr_SetNone` are also
properly handled that way; this would fix #27794 as a side-effect, but a few
lines will need to be changed (in Objects/descrobject.c) for this to work. Such
changes are not included with the patch.
Thoughts, concerns, opinions, ideas? Maybe something I didn't think of?
----------
components: Interpreter Core
files: change_attr_error_messages_1.patch
keywords: patch
messages: 273300
nosy: ebarry, r.david.murray, xiang.zhang, ztane
priority: normal
severity: normal
stage: patch review
status: open
title: Change bare AttributeError messages to be more informative
type: enhancement
versions: Python 3.6
Added file: http://bugs.python.org/file44180/change_attr_error_messages_1.patch
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<http://bugs.python.org/issue27823>
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