If/then style question

[Jean-Michel Pichavant]

John Gordon wrote:
> (This is mostly a style question, and perhaps one that has already been
> discussed elsewhere.  If so, a pointer to that discussion will be
> appreciated!)
>
> When I started learning Python, I wrote a lot of methods that looked like
> this:
>
>
>   def myMethod(self, arg1, arg2):
>
>     if some_good_condition:
>
>       if some_other_good_condition:
>
>         if yet_another_good_condition:
>
>           do_some_useful_stuff()
>           exitCode = good1
>
>         else:
>           exitCode = bad3
>
>       else:
>         exitCode = bad2
>
>     else:
>       exitCode = bad1
>
>     return exitCode
>
>
> But lately I've been preferring this style:
>
>
>   def myMethod(self, arg1, arg2):
>
>     if some_bad_condition:
>       return bad1
>
>     elif some_other_bad_condition:
>       return bad2
>
>     elif yet_another_bad_condition:
>       return bad3
>
>     do_some_useful_stuff()
>     return good1
>
> I like this style more, mostly because it eliminates a lot of indentation.
>
> However I recall one of my college CS courses stating that "one entry,
> one exit" was a good way to write code, and this style has lots of exits.
>
> Are there any concrete advantages of one style over the other?
>
> Thanks.
>
>   

What about,


def myMethod():
    for condition, exitCode in [
            (cond1, 'error1'),
            (cond2, 'very bad error'),
    ]:
        if not condition:
            break
    else:
       do_some_usefull_stuff() # executed only if the we never hit the 
break statement.
       exitCode = good1

    return exitCode

This version uses the 'for ... else' statement. You can easily add 
conditions by simply adding a line in the list, that's it.
Note that this code uses a shadow declaration of exitCode in the for 
loop. If you're not comfortable with that, you'll have to use a properly 
'declared' variable retCode and write retCode = exitCode before 
breaking. Actually I would advise to do so.

JM