Create a race in Python?

I'm very new to python 3. As an assignment, I am supposed to make a race in python basic Syntax and without importing any other additional function, where 3 mice are racing with different odds of winning.

from random import randint
import time


def race():
    z = '----{,_,">'  # The mouse.
    j = ' '
    print('\t'*13, '|')  # The finish line. Very sophisticated.
    while len(z) < 50:
        time.sleep(1)
        #or k in range(3):
        x = randint(1, 6)
        j = ' ' * x
        z = j + z
        print("\r" + str(z), end="")  # For clearing printed text. I prefer not to import os.

As you might see, I've managed to make one; Two to go. But I've scratching my head for three hours on how to do it, that is how to make them go simultaneously ... Any help will be appreciated.