Question

I have some code like:

import math, csv, sys, re, time, datetime, pickle, os, gzip
from numpy import *

x = [1, 2, 3, ... ]
y = sum(x)

The sum of the actual values in x is 2165496761, which is larger than the limit of 32bit integer. The reported y value is -2129470535, implying integer overflow.

Why did this happen? I thought the built-in sum was supposed to use Python’s arbitrary-size integers?

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_{See How to restore a builtin that I overwrote by accident? if you’ve accidentally done something like this at the REPL (interpreter prompt).}

Answer 1

The reason why you get this invalid value is that you’re using np.sum on a int32. Nothing prevents you from not using a np.int32 but a np.int64 or np.int128 dtype to represent your data. You could for example just use

x.view(np.int64).sum()

On a side note, please make sure that you never use from numpy import *. It’s a terrible practice and a habit you must get rid of as soon as possible. When you use the from ... import *, you might be overwriting some Python built-ins which makes it very difficult to debug. Typical example, your overwriting of functions like sum or max…