[Tutor] for/else question

[Jeff Shannon]

Gabriel Cooper wrote:

> Secondly, isn't 
> breaking out of a loop considered "bad programming"? Much like GOTO's? 

Actually, no it's not.  Indeed, one of the recommended idioms in 
Python (to replace the do ... while loop of some other languages) is:

while 1:
     do_stuff()
     if (condition):
         break

The normal 'while (condition)' loop performs an action 0 or more 
times, while the loop above performs an action 1 or more times.  This 
prevents you from needing to initialize variables (say, reading from a 
file to determine the condition) before the while loop and then again 
inside of the while loop.

> So... yeah... Do /you/ use "else" with for loops? If so, when?

I seem to recall a discussion of this on comp.lang.python some time 
ago, which intimated that it was included as much for symmetry (with 
if/else) as for practical need.  (The implementation of code suites is 
such that it is essentially free -- 'else' works the same whether it 
follows a 'for' or an 'if'.)

That said, I can see cases where it's important to know whether you've 
broken out of a loop or not.  You might need to take an action only if 
there are no errors in your loop, for instance.  You could use a 
sentinel variable, but it's cleaner to avoid that, and for/else allows 
you to avoid it.

Jeff Shannon
Technician/Programmer
Credit International