# Cleaning up conditionals

Deborah Swanson python at deborahswanson.net
Fri Dec 30 18:00:02 EST 2016

```BartC wrote:
> Sent: Friday, December 30, 2016 2:11 PM
>
> On 30/12/2016 21:20, Deborah Swanson wrote:
> > I've already learned one neat trick to collapse a conditional:
> >
> > 	a = expression1 if condition else expression2
> >
> > Here I have a real mess, in my opinion:
> >
> > 	if len(l1[st]) == 0:
> >           if len(l2[st]) > 0:
> >               l1[st] = l2[st]
> >           elif len(l2[st]) == 0:
> >               if len(l1[st]) > 0:
> >                   l2[st] = l1[st]
>
> This doesn't make sense. The main block is executed when
> len(l1[st]) is
> 0, but you're testing for len(l1[st])>0 in the last if
> statement (which
> can't see the assignment to l1[st], so can never be true).
> Try writing it out on paper using A and B instead l1[st] and
> l2[st] as
> they look confusing.
>
> You might also be evaluating len(l2[st]) twice.
>
> --
> Bartc

Oops, indentation was messed up when I copied it into the email. Should
be this:

if len(l1[st]) == 0:
if len(l2[st]) > 0:
l1[st] = l2[st]
elif len(l2[st]) == 0:
if len(l1[st]) > 0:
l2[st] = l1[st]

```