list.index crashes when the element is not found

[s0suk3 at gmail.com]

On May 2, 3:26 pm, TkNeo <tarun.... at gmail.com> wrote:
> On May 2, 2:49 pm, Jeff <jeffo... at gmail.com> wrote:
>
> > The generally used idiom for that is:
>
> > lst = ['a', 'b', 'c']
> > if 'a' in lst:
> >   foo = lst.index('a')
>
> Jeff - Gracias !!
>
> I am fairly new to python. Thanks for the example code snippet above.
> It is the same amount of code as receiving -1 and then checking for
> doing an "if else" for -1 so now i don't feel bad. But, being new to
> this paradigm, raising of an exception when it can't find the element
> appears to be weird to me for some unexplainable reason.

I don't know how Python looks up internally 'a' in the list in the
statement "if 'a' in lst: ... ," but just from common sense, I think
it would have to do the work of finding it twice, first in the
statement "'a' in lst," and then in the statement "lst.index('a')." If
you had a lot of elements in the list, and/or you were looping a lot
of times to find a lot of things, it'd be better to do the try/except
form.