[Python-ideas] except expression

[Ethan Furman]

On 02/17/2014 03:54 PM, Chris Angelico wrote:
> On Tue, Feb 18, 2014 at 9:26 AM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
>> There's no logical difference between not generating
>> a result at all, and generating a result of None and
>> then throwing it away.
>>
>> The same thing applies here:
>>
>>     menu.remove(mint) except ValueError: pass
>>
>> This says exactly what the programmer means: "Remove
>> mint from the menu if it's there, otherwise do nothing."
>
> In a statement context, it's possible to say "otherwise do nothing".
> An if without an else does this, as does putting 'pass' in certain
> places.
>
> But in an expression context, there are 'two possibility'. Either some
> kind of value is returned, or an exception is raised. (At least, I
> don't think there are any other options. Harry Hoo, not the Spanish
> Inquisition.) What should happen here:
>
> func(menu.remove(mint) except ValueError: pass)
>
> If remove() raises ValueError, should func be called? If so, with what
> argument? (Note that it's because English is happy with "passing"
> arguments to functions that I was happy with the notation "except
> ValueError pass None", but that's using pass as a syntactic element,
> in place of the colon.)

Yes, func should be called, and it should be called with no arguments.

--
~Ethan~