Debugging reason for python running unreasonably slow when adding numbers

[Weatherby,Gerard]

Moving the generator out:

import timeit

thedata = [i for i in range(1_000_000)]
def sum1():
    s = 0
    for i in thedata:
        s += i
    return s

def sum2():
    return sum(thedata)

print('For Loop Sum:', timeit.timeit(sum1, number=100))
print( 'Built-in Sum:', timeit.timeit(sum2, number=100))

---
For Loop Sum: 6.984986504539847
Built-in Sum: 0.5175364706665277

From: Weatherby,Gerard <gweatherby at uchc.edu>
Date: Wednesday, March 15, 2023 at 1:09 PM
To: python-list at python.org <python-list at python.org>
Subject: Re: Debugging reason for python running unreasonably slow when adding numbers
Sum is faster than iteration in the general case.

Lifting a test program from Stack Overflow https://stackoverflow.com/questions/24578896/python-built-in-sum-function-vs-for-loop-performance,


import timeit

def sum1():
    s = 0
    for i in range(1000000):
        s += i
    return s

def sum2():
    return sum(range(1000000))

print('For Loop Sum:', timeit.timeit(sum1, number=100))
print( 'Built-in Sum:', timeit.timeit(sum2, number=100))

---

For Loop Sum: 7.726335353218019
Built-in Sum: 1.0398506000638008

---


From: Python-list <python-list-bounces+gweatherby=uchc.edu at python.org> on behalf of David Raymond <David.Raymond at tomtom.com>
Date: Wednesday, March 15, 2023 at 11:46 AM
To: python-list at python.org <python-list at python.org>
Subject: RE: Debugging reason for python running unreasonably slow when adding numbers
*** Attention: This is an external email. Use caution responding, opening attachments or clicking on links. ***

> Then I'm very confused as to how things are being done, so I will shut
> up. There's not enough information here to give performance advice
> without actually being a subject-matter expert already.

Short version: In this specific case "weights" is a 5,147 element list of floats, and "input" is a 10 element list of integers which has the indexes of the 10 elements in weights that he wants to add up.

sum_ = 0
for key in input:
    sum_ += weights[key]

vs

sum_ = sum(weights[key] for key in input)

vs... other ways
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