test.py

import sys

def isprime(p, plist):
    max = p ** 0.5
    for i in range(0, len(plist)):
        if max < plist[i]:
            break
        if p % plist[i] == 0:
            return False
    return True

def nprimeslist(n):
    plist = []
    i = 2
    while len(plist) < n:
        if isprime(i, plist):
            plist.append(i)
        i += 1
    return plist

def nthprime(n):
    plist = nprimeslist(n)
    return plist[n - 1]

def main():
    if (len(sys.argv) != 2):
        print "Usage: %s number" % sys.argv[0]
        sys.exit(1)
    n = int(sys.argv[1])
    p = nthprime(n)
    print "The %dth prime is %d" % (n, p)

if __name__ == "__main__":
    main()