how to use bool

[Chris Mellon]

On 03 Jan 2008 16:09:53 GMT,  <tinnews at isbd.co.uk> wrote:
>
> jimgardener at gmail.com wrote:
> > hi, i have some code where i set a bool type variable and if the value
> > is false i would like to return from the method with an error msg..
> > being a beginner I wd like some help here
> >
> > class myclass:
> >      .........
> >     def  mymethod(self):
> >              success=True
> >              msg="all validation OK"
> >              success=validateSthing()
> >              if(success==False):
> >                    msg="sthing failed"
> >                    return (success,msg)
> >
> >              dosomeprocessing()
> >              .....
> >              success=validateSthingelse()
> >              if(success==False):
> >                    msg="sthingelse  failed"
> >                    return (success,msg)
> >              domoreprocessing()
> >               ....
> >                return(success,msg)
> >
> > i would like to know if this way of doing this is OK..I have need of
> > many kinds of validations in this ..is there a better way of doing
> > this ?
> >
> With my philosophical programming hat on the first thing I'd say (as a
> fairly beginning python programmer) is "avoid multiple returns from a
> function/method if at all possible".  They breed all sorts of problems
> and errors, in particular if there's any clearing up to do you have to
> do it in lots of places (or you forget it in some places).
>

This advice is highly controversial, and in the presence of exceptions
it is, at best, voodoo coding. Since your function can exit at any
point whether you do it intentionally or not, if you have crucial
cleanup it's best to write your code in a way that does it correctly
even if you return early. Following this style also often leads to odd
contortions, like extra layers of indentation, and a proliferation of
temporary flags and value-holders that aren't necessary if you write
the code in a more straight forward manner.

Make your decisions on a case by case basis of complexity,
readability, and reliability instead of following pronouncements from
on high (especially decades old pronouncements made in a different
context). Forcing a single return site in the code below adds
complexity, arguable harms readability, and provides *zero* benefit in
the code at hand.

> So:-
>
>     def  mymethod(self):
>         msg="sthing failed"
>         success=validateSthing()
>         if success:
>             dosomeprocessing()
>             .....
>             success=validateSthingelse()
>             if success:
>                 domoreprocessing()
>                 ....
>                 msg="all validation OK"
>         return (success,msg)
>
> I've lost the different messages for different errors but you get the
> idea.
>
>
> "if success:" rather than "if (success==True)", more readable.  For
> the opposite "if not success:".
>
>
>
> --
> Chris Green
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>