module alias in import statement

[ast]

hello

>>> import tkinter as tk
>>> import tk.ttk as ttk

Traceback (most recent call last):
  File "<pyshell#3>", line 1, in <module>
    import tk.ttk as ttk
ImportError: No module named 'tk'


of course

>>> import tkinter.ttk as ttk

works

Strange, isn't it ?