title: How to set PYTHONPATH in Centos 7?
body: <p>In Centos 7 system, what is the default pythonpath enviroment?
  Before I make any pythonpath setting, the command "echo $PYTHONPATH" gives no output. After I make the following setting:</p>
  
  <pre><code>PYTHONPATH="{$PYTHONPATH}:/usr/lib/python2.7/site-packages:/usr/lib64/python2.7/site-packages/pandas:/app/anaconda2/pkgs"
  export PYTHONPATH=$PYTHONPATH:/app/Jade
  </code></pre>
  
  <p>the command "echo $PYTHONPATH" gives the following output:</p>
  
  <pre><code>:/app/Jade
  </code></pre>
  
  <p>I don't understand why before "/app/Jade" there is an extra colon (:). And what is the correct way to set PYTHONPATH?</p>
  
  <p>Best regards.</p>
  
  <p>Yeping Sun</p>