How to let a loop run for a while before checking for break condition?

[Hendrik van Rooyen]

"Hendrik van Rooyen" <mail at microcorp.co.za> wrote:

8<-------------------------------------

Here are some more results, three runs without, and three with a comment in the
body of the interesting loop:
(a summary follows the detail)

> python junk.py

0x5000001
Loop 1 Elapsed time is: 31.2168951035
Loop 1 used           : 16.39
Time out used was     : 28
comment removed from Loop 1

0x5000001
Loop 2 Elapsed time is: 75.8846828938
Loop 2 used           : 37.93

> python junk.py

0x5000001
Loop 1 Elapsed time is: 31.3769760132
Loop 1 used           : 16.1
Time out used was     : 28
comment removed from Loop 1

0x5000001
Loop 2 Elapsed time is: 76.4928090572
Loop 2 used           : 38.23

> python junk.py

0x5000001
Loop 1 Elapsed time is: 34.8213500977
Loop 1 used           : 18.24
Time out used was     : 28
comment removed from Loop 1

0x5000001
Loop 2 Elapsed time is: 82.6038169861
Loop 2 used           : 39.13

> python junk.py

0x5000001
Loop 1 Elapsed time is: 36.7637741566
Loop 1 used           : 18.81
Time out used was     : 28
comment inserted into Loop 1

0x5000001
Loop 2 Elapsed time is: 77.6277718544
Loop 2 used           : 38.82

> python junk.py

0x5000001
Loop 1 Elapsed time is: 37.6858890057
Loop 1 used           : 19.71
Time out used was     : 28
comment inserted into Loop 1

0x5000001
Loop 2 Elapsed time is: 76.0855400562
Loop 2 used           : 38.04

> python junk.py

0x5000001
Loop 1 Elapsed time is: 35.0458369255
Loop 1 used           : 18.32
Time out used was     : 28
comment inserted into Loop 1

0x5000001
Loop 2 Elapsed time is: 75.850135088
Loop 2 used           : 37.9

Summary of results:

Without comment:
Average elapsed time calculated by hand:  32.47
Average clock.clock() time :                    16.91
With comment:
Average elapsed time calculated by hand:  36.39
Average clock.clock() time :                    18.95
Normal loop performance over 6 runs:
Average elapsed time calculated by hand:  77.42
Average clock.clock() time :                    38.34


Conclusion 1:  The lower level test for the signal is far more efficient than
the Python comparison. - these kind of shenanigans are well worth while if the
loop is known to be a long running one.
Conclusion 2:  The setting of the appropriate time out is a PITA... (any ideas?)
Conclusion 3:  Don't put comments in the body of long running loops...
Conclusion 4:  (from earlier in the thread) - using calls are expensive...
Conclusion 5:  I learnt something - Thank you all...

Off topic Question - I see that giving the signal.alarm a float instead of an
integer gives a deprecation warning - does anybody know why this was decided? (I
was trying to do a binary search...)

Here is Claudio's code as I have hacked it:

import signal, time

def func1(timeout):

     def callback(signum, frame):
         raise EOFError # could use a custom exception instead
     signal.signal(signal.SIGALRM, callback)
     signal.alarm(timeout)

     count = 0
     try:
         while 1:
# this is a comment in the body of the loop
             count += 1
     except EOFError:
         while True:
             count += 1
             if count > 0x5000000:
                 break
     print hex(count)

def func2():

     count = 0
     while True:
         count += 1
         if count > 0x5000000:
             break
     print hex(count)

def func3():
    return 0

timeout = 28
print
startTime = time.time()
start_use = time.clock()
func1(timeout)
eltime = time.time() - startTime
utime = time.clock() - start_use
print "Loop 1 Elapsed time is:", eltime
print "Loop 1 used           :", utime
print "Time out used was     :", timeout
print "comment inserted into Loop 1"

print
startTime = time.time()
start_use = time.clock()
func2()
eltime = time.time() - startTime
utime = time.clock() - start_use
print "Loop 2 Elapsed time is:", eltime
print "Loop 2 used           :", utime
print

- Hendrik