STINNER Victor added the comment:
> try:
> cls.meth()
> except AttributeError as exc:
> if exc.attr != 'meth':
> raise
What if cls.__getattr__('meth') calls a completly unrelated function which also
raises AttributeError(attr='meth') but on a different object? I would also
expect an "obj" attribute, a reference to the object which doesn't have
attribute.
But AttributeError can be raised manually without setting attr and/or obj
attribute. So the best test would look to something like:
if exc.obj is cls and exc.attr is not None and exc.attr != 'meth':
raise
The test is much more complex than expected :-/ Maybe it's simpler to split the
code to first get the bounded method?
try:
meth = cls.meth
except AttributeError:
...
meth()
Or check first if cls has the attribute 'meth' with hasattr(cls, 'meth')?
--
About attr/obj attribute not set, an alternative is to add a new
BetterAttributeError(obj, attr) exception which requires obj and attr to be
set, it inherits from AttributeError.
class BetterAttributeError(AttributeError):
def __init__(self, obj, attr):
super().__init__('%r has no attribute %r' % (obj, attr)
self.obj = obj
self.attr = attr
It would allow a smoother transition from "legacy" AttributeError to the new
BetterAttributeError.
The major issue with keeping a strong reference to the object is that Python 3
introduced Exception.__traceback__ which can create a reference cycle if an
exception is stored in a local variable somewhere in the traceback. It's a
major pain point in asyncio. In asyncio, the problem is more likely since
exceptions are stored in Future objects to be used later.
----------
nosy: +haypo
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue18156>
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