[Python-Dev] PEP 463: Exception-catching expressions

Chris Angelico rosuav at gmail.com
Sat Feb 22 13:49:37 CET 2014

On Sat, Feb 22, 2014 at 11:14 PM, Stephen J. Turnbull
<stephen at xemacs.org> wrote:
> Antoine Pitrou writes:
>  > On Sat, 22 Feb 2014 22:13:58 +1100
>  > Chris Angelico <rosuav at gmail.com> wrote:
>  > > hasattr(x,"y") <-> (x.y or True except AttributeError: False)
>  > But it's not the same. hasattr() returns a boolean, not an arbitrary
>  > value.
> I think he meant
>     hasattr(x,"y") <-> (x.y and True except AttributeError: False)

No, I meant 'or' to ensure that an attribute holding a false value
doesn't come up false. But if you really want a boolean, just wrap it
up in bool().

My main point, though, was that most usage of hasattr is probing just
before something gets used - something like this:

if hasattr(obj, "attr"):
    blah blah obj.attr
    maybe use a default or maybe do nothing

Some cases could become except-expressions; others could become
try/except statements. In each case, the loss would be small. I'm not
saying hasattr should be removed, just that it wouldn't have a strong
case if it didn't already exist.


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