[Tutor] List comprehension question

[Richard D. Moores]

On Fri, Nov 12, 2010 at 02:11, Steven D'Aprano <steve at pearwood.info> wrote:
> Richard D. Moores wrote:
>
>> I find using that at the interactive prompt a bit onerous -- lots of
>> copy and pasting. And doubly so when comparing times for 2 or more
>> functions.
>
> Does your Python not support readline? Normally, if you press UP ARROW or
> DOWN ARROW, Python will cycle through the previous interpreter lines.

Do you mean my IDE? IDLE does that with Alt+P and Alt+N. I'm dealing
with multi-line functions, not single lines. If I paste a function at
the prompt, IDLE will bring the whole thing back with Alt+P. Problem
is, IDLE isn't my IDE -- Wing is.

> Another approach is to write helper functions, or use string interpolation,
> to make it easy to re-use code:
>
> setup = "from __main__ import %s as func"
> test = "func(1000)"
> t1 = Timer(test, setup % "my_func")
> t1 = Timer(test, setup % "your_func")
>
> A third approach might be to treat your testing as a script. Put all your
> test code in a module, and then run it:
>
> python time_test.py

OK, but why can't I do what the timeit doc suggests, only put 2 or
more functions in the file, as I do here:
<http://tutoree7.pastebin.com/84u1fkgA>

def test():
    "Stupid test function"
    L = []
    for i in range(100):
        L.append(i)

if __name__=='__main__':
    from timeit import Timer
    t = Timer("test()", "from __main__ import test")
    print t.timeit()

>> The timeit doc gave me the obvious idea of how to avoid the prompt and
>> also easily compare the times of 2 or more functions. I'd like to know
>> if doing it this way is correct: Please see
>> <http://tutoree7.pastebin.com/84u1fkgA>
>
> You're vulnerable to statistical outliers (which are remarkably common on
> multi-tasking operating systems!) cause by the OS calling some other program
> in the middle of yours. Call each time test three or five times, and use the
> smallest.

Sure, I do that with the for loops, don't I?

>> Huh. Just realized that this timing method doesn't include the 5
>> repeats called for by Steven's method. So how about using a for loop?
>> As in <http://tutoree7.pastebin.com/J8bPKUqC>.
>
> You're still re-inventing the wheel. timeit already includes a method for
> doing exactly that: repeat. From the documentation:
>
>    def repeat(self, repeat=default_repeat, number=default_number):
>        """Call timeit() a few times.
>
>        This is a convenience function that calls the timeit()
>        repeatedly, returning a list of results. ...

I'm sorry, Steven, but I could you revise this code to use repeat=5
instead of the for loop? I can't see how to do it.

if __name__=='__main__':
    from timeit import Timer
    for y in range(5):
        t = Timer("proper_divisors_sum1(500000)", "from __main__
import proper_divisors_sum")
        print round(t.timeit(number=10000),3)

Thanks,

Dick