Python: "global name 'time' is not defined"

I'm writing a silly program in python for a friend that prints "We are the knights who say 'Ni'!". then sleeps for 3 seconds, and then prints "Ni!" twenty times at random intervals using the random module's uniform() method. Here's my code:

from time import sleep
import random

def knights_of_ni():
    generator = random.Random()
    print "We are the knights who say 'ni'."
    sleep(3)
    for i in range(0,20):
        print "Ni!"
        sleep(generator.uniform(0,2))

I've tried to import this module by typing in the interpreter from silly import knights_of_ni() and import silly, then calling the function with either knights_of_ni() or silly.knights_of_ni() (respectively), but I always get the same exception:

 NameError: global name 'time' is not defined

What is causing this error and how can I fix my code?

Edit: quite frankly, I'm not sure what problem I was having either. I ran the code the next morning and it worked just fine. I swear that the code produced errors last night... Anyway, thanks for your insight.