title: how to add the path to PYTHONPATH in google colab
body: <p>how to execute the following command in google colab.
  <code>export PYTHONPATH=/project/pylib/src:$PYTHONPATH</code></p>
  
  <p><code>!export PYTHONPATH=/project/pylib/src:$PYTHONPATH</code>it is not affect.</p>