On 24/08/2010 00:05, Benjamin Peterson wrote:
2010/8/23 Michael Foord<fuzzy...@voidspace.org.uk>:
On 23/08/2010 23:55, Benjamin Peterson wrote:
2010/8/23 Raymond Hettinger<raymond.hettin...@gmail.com>:
On Aug 23, 2010, at 1:13 PM, Benjamin Peterson wrote:
2010/8/23 Michael Foord<fuzzy...@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.
One says "does this object have attribute y" the other fetches attribute y.
I'm amazed they don't look different to you. Given Python's object model
there is no reason that the first *should* fetch the attribute to determine
that it is present, *except* for the dynamic attribute creation of
__getattr__ and __getattribute__.
Actually, I'd say given Python's object model, you have to have the
attribute in hand to determine that it is present.
For properties there is *no reason* why code should be executed merely in
order to discover if the attribute exists or not.
Properties are allowed to raise AttributeError, so you technically
have to execute it.
Properties are allowed to do whatever the heck they want. That doesn't
mean that you have to execute code to determine whether they exist or not.
If fetching an attribute raises an AttributeError it doesn't mean that
attribute doesn't exist (although I admit that at the moment this is
exactly what hasattr uses to mean) it just means that fetching that
attribute raised an AttributeError. Even if you allow other exceptions
to propagate you are still left with the fact that an AttributeError
raised as a bug will still be silenced and interpreted as meaning that
hasattr should just return False.
Michael Foord
--
http://www.ironpythoninaction.com/
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