def primeSieve(x):
'''
Generates a list of odd integers from 3 until input, and crosses
out all multiples of each number in the list.
Usage:
primeSieve(number) -- Finds all prime numbers up until number.
Returns: list of prime integers (obviously).
Time: around 1.5 seconds when number = 1000000.
'''
numlist = range(3, x+1, 2)
counter = 0 # Keeps count of index in while loop
backup = 0 # Used to reset count after each iteration and keep count outside of while loop
for num in numlist:
counter = backup
if num != 0:
counter += num
while counter <= len(numlist)-1: # Sifts through multiples of num, setting them all to 0
numlist[counter] = 0
counter += num
else: # If number is 0 already, skip
pass
backup += 1 # Increment backup to move on to next index
return [2] + [x for x in numlist if x]
