Sieve of Erastothenes

sieve.py

from math import sqrt

# Sieve of Erastothenes

def sieve(n):
    candidates = list(range(n))

    # We only need to check up to the square root of n
    upto = int(sqrt(n)) + 1

    # Loop over the candidates, marking out each multiple as None.
    for i in list(range(2, upto)):
        if not candidates[i]:
            continue
        # mark out each multiple of i
        for x in range(2 * i, n, i):
            candidates[x] = None

    # Filter out non-primes and return the list.

    return list(filter(lambda x : x != None, candidates))[2:]

print(sieve(30))