title: No module named ... in PyCharm (import error)
body: <p>I am using PyCharm on MAC to import some packages by</p>
  
  <pre><code>import pymongo
  import bson
  </code></pre>
  
  <p>However the error is <code>ModuleNotFoundError: No module named 'pymongo'</code></p>
  
  <p>The packages are installed successfully and there is nothing wrong when running them in the command line
  I also checked the Interpreter Configuration in Pycharm, fixed to Python 3.6(my only version of Python 3)</p>
  
  <p>Also, when I use <code>pip3 freeze</code> it indicates that these packages are successfully installed</p>
  
  <p>How can I fix this problem?</p>