[Python-Dev] 'hasattr' is broken by design

[Benjamin Peterson]

2010/8/23 Raymond Hettinger <raymond.hettinger at gmail.com>:
>
> On Aug 23, 2010, at 1:13 PM, Benjamin Peterson wrote:
>
>> 2010/8/23 Michael Foord <fuzzyman at voidspace.org.uk>:
>>> To me hasattr *looks* like a passive introspection function, and the fact
>>> that it can trigger arbitrary code execution is unfortunate - especially
>>> because a full workaround is pretty arcane.

hasattr(x, "y") doesn't look any more passive to me the x.y.

>
> Well said.  The surprise to me in the OP's example was that
> the property() was executed.  Regular methods aren't run
> by hasattr() so it's hard to remember that when writing code using hasattr().

Hard to remember compared to what?

>
> That is especially unfortunate because someone turning a regular
> attribute into a property may be doing so long after client code has
> been written (IIRC, that was a key use case for properties).
> IOW, the user of the hasattr() may have had no way
> of knowing that an exception could ever be raised
> (because it is perfectly safe with regular attributes and methods).

Better to raise an exception into unexpecting code that to have subtly
different lookup rules between getattr and hasattr.


-- 
Regards,
Benjamin