title: Multiple versions of python when installing a package with aptitude
body: <p>On a lab machine where I can't just go clobbering things, there appears to be more than one version of python installed.  </p>
  
  <p>If I python --version I see 2.7.1.   </p>
  
  <p>I've installed numpy via "apt-get install numpy" and it says it is installed, but when I try to import it it isn't found.  </p>
  
  <p>When I do a find on the machine for numpy I see it in the /usr/lib/python2.5/site-packages/numpy folder.  I assume this is the problem... that apt-get put it in the 2.5 version instead of the 2.7.  </p>
  
  <p>How do I resolve this?  Is there a way to tell apt-get which python I'm talking about when I do an install?  Or do I abandon aptitude and use pip or something?</p>