[Python-ideas] except expression

[Rob Cliffe]

On 18/02/2014 22:56, Nick Coghlan wrote:
>
>
> On 19 Feb 2014 06:56, "Chris Angelico" <rosuav at gmail.com 
> <mailto:rosuav at gmail.com>> wrote:
> >
> > My script is currently _very_ simplistic. It looks *only* for
> > assignments, so it won't find something like this:
> >
> > try:
> >     foo.append(args[0])
> > except IndexError:
> >     foo.append('')
> >
> > which is correct, because it's impossible to know whether foo.append()
> > will raise IndexError. (Chances are it won't, especially if we know
> > foo is a list, for instance.) It's not safe to directly translate that
> > sort of thing. It might, however, be something worth improving, as it
> > narrows the scope of the except clause. But if that same code is
> > written thus:
> >
> > try:
> >     tmp = args[0]
> > except IndexError:
> >     tmp = ''
> > foo.append(tmp)
> >
> > then the script _will_ find it, and then it really is a candidate 
> for editing.
>
> This example should go in the PEP - the except clause in the example 
> code is almost certainly too broad, but the fix is rather ugly.
>
> With the PEP, the except clause can easily be moved inside the 
> expression so it doesn't cover the append() call:
>
>     foo.append((args[0] except IndexError: ""))
>
> Cheers,
> Nick.
>
Beautiful catch, Nick!  Shows that this proposal not only gives a neater 
way of writing code without changing the semantics, but may actually 
point the way to _improving_ existing (or new) code.
Rob Cliffe
>
>
>
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