In python-mode plugin NameError: name 'pymode' is not defined

Question

I have just installed the python-mode plugin by vundle

deal with /home/lucas/.vim/autoload/pymode/doc.vim gets error:
line 3:
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: No module named 'pymode'
[Pymode]: error: No name/symbol under cursor!

this is my first time to use this plugin, does this mean there are some mistakes with installing the python-mode plugin?