Debugging reason for python running unreasonably slow when adding numbers

[Thomas Passin]

On 3/14/2023 3:48 AM, Alexander Nestorov wrote:
> I'm working on an NLP and I got bitten by an unreasonably slow behaviour in Python while operating with small amounts of numbers.
> 
> I have the following code:
> 
> ```python
> import random, time
> from functools import reduce
> 
> def trainPerceptron(perceptron, data):
>    learningRate = 0.002
>    weights = perceptron['weights']
>    error = 0
>    for chunk in data:
>        input = chunk['input']
>        output = chunk['output']
> 
>        # 12x slower than equivalent JS
>        sum_ = 0
>        for key in input:
>            v = weights[key]
>            sum_ += v
> 
>        # 20x slower than equivalent JS
>        #sum_ = reduce(lambda acc, key: acc + weights[key], input)
> 
>        actualOutput = sum_ if sum_ > 0 else 0
> 
>        expectedOutput = 1 if output == perceptron['id'] else 0
>        currentError = expectedOutput - actualOutput
>        if currentError:
>            error += currentError ** 2
>            change = currentError * learningRate
>            for key in input:
>                weights[key] += change

[snip]
Just a speculation, but the difference with the javascript behavior 
might be because the JS JIT compiler kicked in for these loops.