[program-l] Re: Python list access speeds
- From: "R Dinger" <rrdinger@xxxxxxxxxx>
- To: <program-l@xxxxxxxxxxxxx>
- Date: Mon, 1 Oct 2012 07:42:47 -0700
Regarding your random tests: reducing time from 7 seconds to 2.7 is still
2.59 times faster and that could be significant.
I vaguely recall your test, but I thought it was much closer.
Richard
----- Original Message -----
From: "Jacob Kruger" <jacob@xxxxxxxxxxxxx>
To: <program-l@xxxxxxxxxxxxx>
Sent: Sunday, September 30, 2012 9:36 PM
Subject: [program-l] Re: Python list access speeds
Reminds me of a test I did - put together two loops where used either
random.random() and converted the result to a number ranging from 1 to 100
sort of manually, and then did the same loop, but using random.randint(1,
100), and got them to both operate like 100000 times, and it was actually
slightly quicker to just use random.random(), but anyway - think difference
was like 2.7 seconds, compared to like 7 seconds.
Stay well
Jacob Kruger
Blind Biker
Skype: BlindZA
'...fate had broken his body, but not his spirit...'
----- Original Message -----
From: "R Dinger" <rrdinger@xxxxxxxxxx>
To: "programming" <program-l@xxxxxxxxxxxxx>
Sent: Monday, October 01, 2012 1:01 AM
Subject: [program-l] Python list access speeds
>I got to thinking about list access speeds when reading replies to Al's
> iterator reset question last week, so I decided to do some testing with
> the
> timeit module. I tested access by subscript and by direct iteration.
>
> I used the following setup code (a list of 500 random numbers) for all the
> tests. The time to execute the setup code is not included in the timing
> tests.
> setup = """
> from random import random
> valList = []
> for i in xrange(500):
> valList.append(random())
> """
>
> The following code fragments were tested each running the loop 1 million
> times.
> stmt1 = """
> for i in range(len(valList)):
> v = valList[i]
> """
> time: 8.01 sec
>
> stmt2 = """
> for i in xrange(len(valList)):
> v = valList[i]
> """
> time: 7.43 sec
>
> stmt3 = """
> for v in valList:
> pass
> """
> time: 2.67 sec
>
> stmt4 = """
> for i, v in enumerate(valList):
> pass
> """
> time: 6.12 sec
>
> So access by subscripting from a list generated by the range function is
> the
> slowest. In the second test using xrange (a generator) helped a little,
> but
> not much. The third test using direct iteration of the list is clearly
> much
> faster. Finally in the last test I used the enumerate object to generate
> the subscripts in case that was needed by the application in addition to
> the
> list value.
>
> The timeit module is quite handy, but be careful it can be quite addictive
> and lead to late nights testing all sorts of code fragments.
>
> Richard
>
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