Working around a lack of 'goto' in python

Roger Binns rogerb at rogerbinns.com
Mon Mar 8 06:09:58 CET 2004


> > What you have is what many other languages allow with integers after break or
> > continue statements.  For example you can do 'break 2' or 'continue 3' to
> > break or continue out of the respective number of enclosing for loops.
>
> Yuck.  Bletch.  Barf.

Care to expand on that?  It is a construct present in shell scripting
as an example  (Googling for "/bin/sh" "break 2" and "continue 2" shows
it in common use, and almost always in exactly the same type of code
OP mentioned and as I show below).

Here is a small contrived example of it in action

for line in lines:
    chars=line  # (contrived)
    for z in chars:
        if z=='!':
            continue 2  # char is special so go to next line
    print chars  #  or some other work

Here is how you conventionally write it without continue 2

for line in lines:
     chars=line
     sawspecial=False
     for z in chars:
         if z=='!':
             sawspecial=True
             break
     if not sawspecial:
         print chars # and other work

Note how at the important point you have to write 'break', despite
thinking 'continue' in your head.  You have to introduce a new
state variable.  As I said, this gets a lot worse if there are
multiple conditions in which you want to break/continue multiple
levels (more variables, more 'continues' where you think 'break'
and vice versa).

Roger





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