[Python-3000] Iterators for dict keys, values, and items == annoying :)

[Guido van Rossum]

On 3/24/06, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
>  > Someone else wrote:
> > > When I was just
> > > first learning Python I thought this would work:
> > >
> > >   for item in select_results:
> > >       ...
> > >   else:
> > >       ... stuff when there are no items ...
> > >
> > > But it doesn't work like that.
>
> I have to agree that's actually a more intuitive use
> of "else" in relation to a for-loop. It's a pity that
> some other word wasn't chosen that would have left
> "else" free for this purpose.
>
> Could something perhaps be done about this in Py3k?
> Blatantly changing the meaning of "else" here might
> be going too far, but maybe some other construct could
> be found that expresses the same intent.

I suspect that this isn't good enough for the crowd who want to
special-case "empty", and in fact the "empty flag" pattern won't work
for them as well. They typically want to do this:

results = query()
if not results:
    print "<h1>No results</h1>"
else:
  print "<h1>Results</h1>"
  print "<table>"
  for value in results:
    print "<tr><td>%s</td></tr>" % value
  print "</table>"

IOW they want to do something *before* entering the for-loop only if
it's not empty.

In this type of use case, casting to list() is totally fine -- if the
list contains more than a few dozen items they'd want to insert
pagination code anyway...

--
--Guido van Rossum (home page: http://www.python.org/~guido/)