Question about modules

Why do I need "from datetime import datetime" in the following code?

import math
import random
import time
from datetime import datetime

def first():
hour = datetime.time(datetime.now()).hour
minute = datetime.time(datetime.now()).minute
second = datetime.time(datetime.now()).second
milisecond = datetime.time(datetime.now()).microsecond/1000
return hour, minute, second, milisecond

I know it won't work without it, but why is that? I tried with only import datetime, it didn't work.
Thanks for the reply in advance

This module looks screwy, but I didn't read the manual. The datetime you imported is a class in the datetime module. Why a constructor for objects of class datetime class is hidden in a method of the class I cannot say.