Debugging reason for python running unreasonably slow when adding numbers
MRAB
python at mrabarnett.plus.com
Mon Mar 20 13:42:44 EDT 2023
On 2023-03-20 15:21, Edmondo Giovannozzi wrote:
>
>> > def sum1():
>> > s = 0
>> > for i in range(1000000):
>> > s += i
>> > return s
>> >
>> > def sum2():
>> > return sum(range(1000000))
>> Here you already have the numbers you want to add.
>
> Actually using numpy you'll be much faster in this case:
>
> § import numpy as np
> § def sum3():
> § return np.arange(1_000_000, dtype=np.int64).sum()
>
> On my computer sum1 takes 44 ms, while the numpy version just 2.6 ms
> One problem is that sum2 gives the wrong result. This is why I used np.arange with dtype=np.int64.
>
> sum2 evidently doesn't uses the python "big integers" e restrict the result to 32 bits.
>
On my computer they all give the same result, as I'd expect.
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