cascading python executions only if return code is 0

[Frank Cui]

> To: python-list at python.org
> From: ned at nedbatchelder.com
> Subject: Re: cascading python executions only if return code is 0
> Date: Sun, 22 Dec 2013 14:49:43 -0500
> 
> On 12/22/13 2:10 PM, Frank Cui wrote:
> > sorry, but what if I need to have different parameters in these functions ?
> 
> Frank, welcome to the group.  Common convention is to put your response 
> below the exiting message, so that the conversation continues down the page.
> 
> (See my answer below... :)
> 
> >
> >
> >  > To: python-list at python.org
> >  > From: breamoreboy at yahoo.co.uk
> >  > Subject: Re: cascading python executions only if return code is 0
> >  > Date: Sun, 22 Dec 2013 19:31:21 +0000
> >  >
> >  > On 22/12/2013 19:17, Roy Smith wrote:
> >  > > In article <mailman.4500.1387739297.18130.python-list at python.org>,
> >  > > Frank Cui <ycui at outlook.com> wrote:
> >  > >
> >  > >> hey guys,
> >  > >> I have a requirement where I need to sequentially execute a bunch of
> >  > >> executions, each execution has a return code. the followed
> > executions should
> >  > >> only be executed if the return code is 0. is there a cleaner or
> > more pythonic
> >  > >> way to do this other than the following ?
> >  > >> if a() == 0: if b() == 0: c()
> >  > >> Thanks for your input.
> >  > >> frank
> >  > >
> >  > > Yup! Just do:
> >  > >
> >  > > a() or b() or c()
> >  > >
> >  > > The "or" operation has what's known as "short-circuit" semantics. That
> >  > > means, if the first operand is true, it doesn't evaluate the second
> >  > > operand. Just make sure that a(), b(), and c() all return something
> >  > > which is true if they succeed and false otherwise.
> >  > >
> >  >
> >  > Really? :)
> >  >
> >  > --
> >  > My fellow Pythonistas, ask not what our language can do for you, ask
> >  > what you can do for our language.
> >  >
> >  > Mark Lawrence
> >  >
> >  > --
> >  > https://mail.python.org/mailman/listinfo/python-list
> >
> >
> 
> The most Python-natural way to deal with your problem would be to have 
> these functions not return status codes at all.  Instead, have them 
> raise an exception if something goes wrong.   Then you can invoke them 
> most naturally:
> 
>      a()
>      b()
>      c()
> 
> Execution will continue as long as no exceptions are raised.  If you 
> need to deal with the failure case also, then:
> 
>      try:
>          a()
>          b()
>          c()
>      except Exception as e:
>          # do something here
> 
> Depending on how you want to deal with failures, you'd probably use your 
> own subclass of Exception, but this is the general idea.
> 
> Return codes can be awkward, especially in Python which has exception 
> integrated so fully into the language, library, and culture.
> 
> -- 
> Ned Batchelder, http://nedbatchelder.com
> 
> -- 
> https://mail.python.org/mailman/listinfo/python-list

Thanks for informing the rules. 		 	   		  
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