Josiah Carlson wrote:
> Ron Adam <[EMAIL PROTECTED]> wrote:
>>I should have said "...should not finalize at the end of the for loop".
>> With generators, you may not want them to finalize before you are done
>>with them, and the same with class's.
>
>
> So you don't use them with a structure that greedily finalizes, and you
> keep a reference to the object exterior to the loop. Seems to be a
> non-issue.
Yes, it should be a non issue.
> The argument over whether blocks should loop, I believe has been had;
> they should. The various use cases involve multi-part transactions and
> such.
I think so now too, I had thought as Nick does earlier this week that
the non-looping version was cleaner, but changed my mind when I realized
that looping blocks could be made to work for those in a simple and
understandable way.
>>try:
>> for x in range(100):
>> for y in range(100):
>> for z in range(100):
>> if x == 25 and y==72 and z==3:
>> raise BreakLoop
>>
>>except BreakLoop: pass
>>print 'x,y,z =', x,y,z
> That is a mechanism, but I like it even less than the one I offered.
> Every time that one wants ot offer themselves the ability to break out
> of a different loop (no continue here), one must create another
> try/except clause, further indenting, and causing nontrivial try/except
> overhead inside nested loops.
>
> A real solution to the problem should (in my opinion) allow the breaking
> of or continuing to an arbitrary for/while/block. Humorously enough,
> Richie Hindle's goto/comefrom statements for Python ("not to be used in
> production code") would allow 90% of the necessary behavior (though the
> lack of timely finalization would probably annoy some people, but then
> again, there is only so much one can expect from a module written as a
> working April Fools joke over a year ago).
>
> - Josiah
I think maybe another alternative is a break buffer or cue. Where you
push a 'break' onto the buffer and then execute a 'break' to break the
current loop, The 'break' in the buffer then breaks the next loop out as
soon as the current loop exits, etc.
for x in range(100):
for y in range(100):
for z in range(100):
if x == 25 and y==72 and z==3:
push_loop(Break,Break) # will break both parent loops
break # break current loop
if push_loop(...) could take a NoBreak, then you can selectively break
outer breaks by how you sequence them.
push_break(None, break) wound not break the y loop, but will break the x
loop above. Can you think of a use case for something like that?
Pushing 'Continues' might also work:
for x in range(100):
for y in range(100):
if x == 25 and y==72:
push_loop(Continue) # will skip rest of parents body
break # break current loop
#code2
#code1
This will break the 'y' loop and skip code2, then continue the 'x' loop
skipping code block 1.
Using a stack for breaks and continues isn't too different than using a
stack for exceptions I think.
Also by making it a function call instead of a command you can have a
function return a Break or Continue object, or None,
for x in range(100):
for y in range(100):
if y == testval:
push_loop(looptest(x,y)): break x loop depending on x,y
break
None's returned would need to be discarded I think for this to work, so
something else would be needed to skip a level.
It needs some polish I think. ;-)
Cheers,
Ron_Adam
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
http://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
