I installed pyqt4 by using Homebrew. But when I import PyQt4 in python interpreter, It said that "No module named PyQt4". Can somebody help me with that?
You have to check which Python you are using. I had the same problem because the Python I was using was not the same one that brew was using. In your command line:

which python
output: /usr/bin/python
which brew
output: /usr/local/bin/brew          //so they are different
cd /usr/local/lib/python2.7/site-packages
ls     //you can see PyQt4 and sip are here
Now you need to add usr/local/lib/python2.7/site-packages to your python path.
open ~/.bash_profile     //you will open your bash_profile file in your editor
Add   'export PYTHONPATH=/usr/local/lib/python2.7/site-packages:$PYTHONPATH'     to your bash file and save it
Close your terminal and restart it to reload the shell
python 
import PyQt4    // it is ok now
ImportError: No module named PyQt4