title: virtualenv : pip doesn't install inside the environment
body: <p>Here I am trying to install some module(consider numpy) in virtualenv environment cv. I trying install it with,</p>
  
  <pre><code>sudo pip3 install numpy
  </code></pre>
  
  <p>it gets inside my normal environment but not the one i created using virtualenv. I keep getting </p>
  
  <pre><code>File "sample.py", line 1, in &lt;module&gt;
      import numpy as np
  ImportError: No module named 'numpy'
  </code></pre>
  
  <p>It works fine in my normal environment. The installed files exist under my /usr/local/lib/python3.5/dist-packages but couldn't find it under .virtualenvs/cv/lib/python3.5/site-packages. I am not sure what I am doing wrong. </p>
  
  <p>I refered couple similar problems and tried it but none worked. I even tried deactivating the env and creating a new one. Let me know if you need any more info. Thanks in advance.</p>
  
  <p>Note: I did activate the environment. When I tried installing again, it says,</p>
  
  <pre><code>Requirement already satisfied: numpy in /usr/local/lib/python3.5/dist-packages
  </code></pre>
  
  <p>It is checking in the normal environment lib folder, not in the virtualenv.</p>