Project Euler p10

p010.py

import time


def is_prime(val, primes_smaller):
    """Determine if a number is prime given a list of all primes less than it."""
    cutoff = int(val**(0.5))
    val_primeness = True
    for testval in primes_smaller:
        if val - (val // testval)*testval == 0:
            val_primeness = False
            break
        if testval >= cutoff:
            break
    return val_primeness


def primes_less_than(n):
    """Find all the primes less than the input."""
    primes = [2]
    for val in range(3,n+1):
        if is_prime(val, primes):
            primes.append(val)
    return primes


def main():
    """Find the sum of all primes less than 2e6."""
    print(sum(primes_less_than(int(2e6))))
#    print(sum(primes_less_than(int(1e5))))

if __name__ == "__main__":
    tstart = time.time()
    main()
    tend = time.time()
    print("total time:", tend - tstart, "s")