title: why am i encountering the " ModuleNotFoundError: No module named 'yaml' " in ROS?
body: <p>I have recently begun to learn ROS.
  whilst running a node file in pycharm, I'm encountering the aforementioned error.</p>
  
  <p>my interpreter is <em>python2.7</em> and I do have <em>yaml</em> installed for <em>python2.7</em>. I have tried adding a path to the <em>yaml</em> folder but it's still not working. I'm using <em>Ubuntu 18.04</em>.</p>
  
  <p>error message in terminal:</p>
  
  <p><a href="https://i.stack.imgur.com/Oo7eJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Oo7eJ.png" alt="enter image description here"></a></p>