Paddy wrote:
> Wijaya Edward wrote:
>> Can we make loops control in Python?
>> What I mean is that whether we can control
>> which loops to exit/skip at the given scope.
>>
>> For example in Perl we can do something like:
>>
>> OUT:
>> foreach my $s1 ( 0 ...100) {
>>
>> IN:
>> foreach my $s2 (@array) {
>>
>> if ($s1 == $s2) {
>> next OUT;
>> }
>> else {
>> last IN;
>> }
>>
>> }
>> }
>>
>> How can we implement that construct with Python?
>>
>
> Python does not use Labels. If you want to quit a single loop then look
> up the Python break statement. If you want to exit deeply nested
> execution then Python has exceptions. this maybe new to a Perl
> programmer so please take time to understand Python exceptions.
>
> There follows a function that you can call from an interactive session
> to explore one type of use for exceptions that is rather like your use
> of Perl labels shown.
>
> ==========================
> class Outer(Exception):
> pass
> class Inner(Exception):
> pass
>
> def skip_loops(y1 = -1, y2 = -1, y3 = -1):
> ''' Shows how to skip parts of nested loops in Python'''
> try:
> for x0 in range(3):
> try:
> for x1 in range(3):
> for x2 in range(3):
> if x2 == y2:
> raise Inner
> if x2 == y3:
> break
> print (x0,x1,x2)
> if x1 == y1:
> raise Outer
> print (x0,x1)
> except Inner:
> print "Raised exception Inner"
> print (x0,)
> except Outer:
> print "Raised exception Outer"
>
> ==========================
>
>>>> skip_loops(y1=2)
> (0, 0, 0)
> (0, 0, 1)
> (0, 0, 2)
> (0, 0)
> (0, 1, 0)
> (0, 1, 1)
> (0, 1, 2)
> (0, 1)
> (0, 2, 0)
> (0, 2, 1)
> (0, 2, 2)
> Raised exception Outer
>>>> skip_loops(y2=2)
> (0, 0, 0)
> (0, 0, 1)
> Raised exception Inner
> (0,)
> (1, 0, 0)
> (1, 0, 1)
> Raised exception Inner
> (1,)
> (2, 0, 0)
> (2, 0, 1)
> Raised exception Inner
> (2,)
>
>
> - Paddy.
> P.S. Welcome to Python!
>
How about a thread on GOTOs ? ;-)
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