title: source activate virtualenv does nothing
body: <p>I installed python through <code>brew install python</code>,then i installed virtualenv by <code>pip install virtualenv</code>.
  then i add 'export PATH=$PATH:/Library/Frameworks/Python.framework/Versions/2.7/bin' to .zshrc.
  And i created a virtual enviroment by <code>virtualenv ENV</code> and no errors.
  But finally i executed <code>source ENV/bin/activate</code> it did nothing.
  (sorry,i can not post images,no requtations,I said nothing is nothing,all is like i never typed something)It looks like this:</p>
  
  <pre>py2 virtualenv ENV
  New python executable in ENV/bin/python
  Installing setuptools,pip...done
  py2 source ./ENV/bin/activate
  py2
  py2 (nothing prompt)
  </pre>
  
  <p>so what's wrong with it?<br>
  thanks a lot.</p>
  
  <p>PS,sorry for my poor english.</p>