Python Overflow error: int too large to convert to C long

Question

I'm a beginner and I'm doing the problems in and while doing the third problem, which is about finding the largest prime factor of 600851475143, I get this error:

Python int too large to convert to C long

plist = [2]


def primes(min, max):
    if 2 >= min:
        yield 2
    for i in xrange(3, max, 2):
        for p in plist:
            if i % p == 0 or p * p > i:
                break
        if i % p:
            plist.append(i)
            if i >= min:
                yield i


def factors(number):
    for prime in primes(2, number):
        if number % prime == 0:
            number /= prime
            yield prime
        if number == 1:
            break

a = 600851475143
print max(factors(a))

Possible duplicate of [OverflowError Python int too large to convert to C long](http://stackoverflow.com/questions/22114088/overflowerror-python-int-too-large-to-convert-to-c-long) — Łukasz Rogalski, Feb 15 '17 at 17:46
I don't, I'm using Windows PowerShell to run that script, and the error shown is in that itself — Oxide, Feb 15 '17 at 17:48
@WillemVanOnsem I think they don't, `xrange` apparently does. — Paul Panzer, Feb 15 '17 at 17:48

score 2 · Accepted Answer · answered Feb 15 '17 at 17:47

Annoyingly, in Python 2, xrange requires its arguments to fit into a C long. 600851475143 is too big for that on your system. You'll have to rewrite your algorithm to not need such a big range, or use a substitute, such as your own xrange implementation, or a while loop with manual counter management.

score -1 · Answer 2 · answered Feb 15 '17 at 17:50

-1

This occurs when the number you are dealing with is greater than sys.maxsize

You could possibly use the numpy module and use a larger data type. Not sure how large you need without checking though.

answered Feb 15 '17 at 17:50

Casey Williams

96
1
8

How to do it without numpy dependency? – jtlz2 Jul 10 '19 at 14:05

Python Overflow error: int too large to convert to C long

2 Answers2