range() is not the best way to check range?

[John Machin]

On 18/07/2006 12:41 PM, Summercoolness at gmail.com wrote:
> it seems that range() can be really slow:
> 
> the following program will run, and the last line shows how long it ran
> for:
> 
> import time
> 
> startTime = time.time()
> 
> a = 1.0
> for i in range(0, 30000):
>     if i in range (0, 10000):
>         a += 1
>     if not i % 1000: print i
> 
> print a, "   ", round(time.time() - startTime, 1), "seconds"
> 
> 
> ---------------------------------
> the last line of output is
> ---------------------------------
> 
> 10001.0     22.8 seconds
> 
> so if i change the line
> 
>     if i in range (0, 10000):
> 
> to
> 
>     if i >= 0 and i < 10000:
> 
> the the last line is
> 
> 10001.0     0.2 seconds
> 
> so approximately, the program ran 100 times faster!
> 
> or is there an alternative use of range() or something similar that can
> be as fast?

Some things to try:
1a. Read what the manual has to say about the range() function ... what 
does it produce?

1b. Read what the manual has to say about time.time() and time.clock(). 
Change over to using time.clock(). Change the round(...., 1) to (say) 4.

Alternatively, use something like this:

     print "%.1f ... %.4f seconds" % (a, time.clock() - startTime)

1c. Repeat the two ways that you tried already.

2. First alternative:

Do this:

     test_range = range(10000)

*once*, just after "a = 1.0".

and change your if test to

     if i in test_range:

3. Now change that to:

     test_range = set(range(10000))

4. Now forget about test_range, and change your if test to this:

     if 0 <= i < 10000:

HTH,
John