multiple breaks

[TP]

Hi everybody,

Several means to escape a nested loop are given here:

http://stackoverflow.com/questions/189645/how-to-break-out-of-multiple-loops-in-python

According to this page, the best way is to modify the loop by affecting the
variables that are tested in the loops. Otherwise, use exception:

"If, for some reason, the terminating conditions can't be worked out,
exceptions are a fall-back plan."

In the following example, is this possible to affect the two iterators to
escape the two loops once one "j" has been printed:

for i in range(5):
for j in range(i):
print j
# I would type "break 2" in shell bash
# In C, I would set j=i-1 and i=4
# In Python, is this possible to affect the two iterators?

Or the only means is to use exception?

Thanks in advance

Julien

--
python -c "print ''.join([chr(154 - ord(c)) for c in '*9(9&(18%.9&1+ ,\'Z
(55l4('])"

"When a distinguished but elderly scientist states that something is
possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong." (first law of AC Clarke)

[Chris Rebert]

Re: multiple breaks

On Thu, Nov 13, 2008 at 2:07 AM, TP <Tribulations@p aralleles.inval idwrote:

Hi everybody,
>
Several means to escape a nested loop are given here:
>

http://stackoverflow.com/questions/189645/how-to-break-out-of-multiple-loops-in-python

>
According to this page, the best way is to modify the loop by affecting the
variables that are tested in the loops. Otherwise, use exception:
>
"If, for some reason, the terminating conditions can't be worked out,
exceptions are a fall-back plan."
>
In the following example, is this possible to affect the two iterators to
escape the two loops once one "j" has been printed:
>

Non-exception alternative:

done = False

for i in range(5):
for j in range(i):
print j

done = True
break

# I would type "break 2" in shell bash
# In C, I would set j=i-1 and i=4
# In Python, is this possible to affect the two iterators?

if done:
break

>
Or the only means is to use exception?

No, you could add a boolean variable and a break condition like above.

Cheers,
Chris
--
Follow the path of the Iguana...

http://rebertia.com

>
Thanks in advance
>
Julien
>
--
python -c "print ''.join([chr(154 - ord(c)) for c in '*9(9&(18%.9&1+ ,\'Z
(55l4('])"
>
"When a distinguished but elderly scientist states that something is
possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong." (first law of AC Clarke)
--

http://mail.python.org/mailman/listinfo/python-list

>

[Marc 'BlackJack' Rintsch]

Re: multiple breaks

On Thu, 13 Nov 2008 11:07:25 +0100, TP wrote:

According to this page, the best way is to modify the loop by affecting
the variables that are tested in the loops. Otherwise, use exception:
>
"If, for some reason, the terminating conditions can't be worked out,
exceptions are a fall-back plan."
>
In the following example, is this possible to affect the two iterators
to escape the two loops once one "j" has been printed:
>
for i in range(5):
for j in range(i):
print j
# I would type "break 2" in shell bash # In C, I would set j=i-1
and i=4
# In Python, is this possible to affect the two iterators?
>
Or the only means is to use exception?

You could put the code into its own, maybe local, function and use
``return``.

Ciao,
Marc 'BlackJack' Rintsch

[Peter Otten]

Re: multiple breaks

TP wrote:

Hi everybody,
>
Several means to escape a nested loop are given here:
>
>

http://stackoverflow.com/questions/1...oops-in-python

>
According to this page, the best way is to modify the loop by affecting
the variables that are tested in the loops. Otherwise, use exception:
>
"If, for some reason, the terminating conditions can't be worked out,
exceptions are a fall-back plan."
>
In the following example, is this possible to affect the two iterators to
escape the two loops once one "j" has been printed:
>
for i in range(5):
for j in range(i):
print j
# I would type "break 2" in shell bash
# In C, I would set j=i-1 and i=4
# In Python, is this possible to affect the two iterators?
>
Or the only means is to use exception?

Here's one way to turn multiple iterators into a single one:

def pairs(n):
for i in range(n):
for k in range(i):
yield i, k

for i, k in pairs(5):
print i, k

I've yet to see an example where a multi-level break would improve the
code's readability. It is typically a speed hack.

Peter

PS: Have a look into the itertools if you consider that approach.

[Steve Holden]

Re: multiple breaks

Chris Rebert wrote:

On Thu, Nov 13, 2008 at 2:07 AM, TP <Tribulations@p aralleles.inval idwrote:

>Hi everybody,
>>
>Several means to escape a nested loop are given here:
>>
>http://stackoverflow.com/questions/1...oops-in-python
>>
>According to this page, the best way is to modify the loop by affecting the
>variables that are tested in the loops. Otherwise, use exception:
>>
>"If, for some reason, the terminating conditions can't be worked out,
>exceptions are a fall-back plan."
>>
>In the following example, is this possible to affect the two iterators to
>escape the two loops once one "j" has been printed:
>>

>
Non-exception alternative:
>
done = False

>for i in range(5):
> for j in range(i):
> print j

done = True
break

> # I would type "break 2" in shell bash
> # In C, I would set j=i-1 and i=4
> # In Python, is this possible to affect the two iterators?

if done:
break

>Or the only means is to use exception?

>
No, you could add a boolean variable and a break condition like above.
>

Though I would have to ask why you would want to. An exception seems
rather cleaner, though of course tastes vary.

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC http://www.holdenweb.com/

[Robert Lehmann]

Re: multiple breaks

On Thu, 13 Nov 2008 02:16:32 -0800, Chris Rebert wrote:

On Thu, Nov 13, 2008 at 2:07 AM, TP <Tribulations@p aralleles.inval id>
wrote:

>>
>In the following example, is this possible to affect the two iterators
>to escape the two loops once one "j" has been printed:
>>

Non-exception alternative:
>
done = False
for i in range(5):
for j in range(i):
print j
done = True
break
if done:
break

Another alternative is explicitly jumping in the outer loop::

for i in range(5): # use xrange for larger ranges
for j in range(i):
print j
break
else:
continue # applies already to the outer loop
break

HTH,

--
Robert "Stargaming " Lehmann