I got a ImportError,help~!

[xlizzard]

HI,
I am a newer to python(my version is 3.1.2),recently I got a IDE named Eric(http://eric-ide.python-projects.org/index.html) to study
and on this main page I downloaded a tutorial named "minibrowser".
http://eric-ide.python-projects.org/tutorials/MiniBrowser/index.html
But when I run this source ,I got the follow Error:
Traceback (most recent call last):
  File "C:\minibrowser\minibrowser\minibrowser.py", line 3, in <module>
    from ui.mainwindow import MainWindow
  File "C:\minibrowser\minibrowser\ui\mainwindow.py", line 10, in <module>
    from Ui_mainwindow import Ui_MainWindow
ImportError: No module named Ui_mainwindow
 
I don't understand what's wrong?!
The folder structure of the source just like this
A.py+
   -B.py
   -C.py
A call B,B call C in the same folder ,and "not found"?
Can anyone help me,thanks a lot~!
 
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