Decently Efficient sieve

from __future__ import print_function
import time
import sys
import math
try:
    import numpypy
except:
    pass
import numpy
def gcd(x,y):
    if x%y == 0:
        return y
    return gcd(y,x%y)
def build_sieve(n):
    nums = numpy.arange(2,n+1,dtype=numpy.int32)
    primes = []
    ct = int(math.sqrt(n))
    sp = int(ct/50)
    x = 2
    count = 0
    tick = 0
    print("\r[%50s]"%("="*tick),end="")
    while x <= ct:
        if x >= tick*sp+sp:
            print("\r[%50s]"%("="*tick),end="")
            tick += 1
            sys.stdout.flush()
        nums = nums[nums%x != 0]
        primes.append(x)
        x = nums[0]
    print("\r"+" "*53,end="\r")
    for x in nums:
        primes.append(x)
    return primes
start = time.time()
primes = build_sieve(int(raw_input("> ")))
elapsed = time.time() - start
print("You took %f seconds to calculate %d primes"%(elapsed,len(primes)))
yeses = set(["yes","y","yeah","yep"])
noes = set(["no","n","nope"])
res = "huh"
while res not in noes and res not in yeses:
    res = raw_input("Would you like to save to a file [y/n]? ").lower()
    if res not in noes and res not in yeses:
        print("Please type y or n")
if res in yeses:
    fname = raw_input("File Name: ")
    f = open(fname,"w")
    count = 0
    l = len(primes)
    sp = int(l/3000)
    for x in primes:
        f.write(str(x))
        f.write("\n")
        if int(count)%sp == 0:
            print("\r%5.1f%%"%(100.0*count/l),end="")
            sys.stdout.flush()
        count += 1
    print("\r"+" "*50,end="\r")
    f.close()
else:
    print("Okay then, goodbye!")