title: Jupyter-notebook failed to import python packages
body: <p>I was trying to use <code>numpy</code> in Jupyter Notebook in a Python3 virtual environment, but the encountered an error.</p>
  <p>In terminal, I did:</p>
  <pre><code>$ python3 -m venv py3env
  $ source py3env/bin/activate
  (py3env)$ jupyter notebook
  </code></pre>
  <p>And on the Jupyter page, I created a new notebook and executed the followings</p>
  <pre><code>!pip install numpy
  import numpy as np
  </code></pre>
  <p>And the resulting output is this:</p>
  <pre><code>Requirement already satisfied: numpy in /Users/MyName/py3env/lib/python3.9/site-packages (1.20.2)
  ---------------------------------------------------------------------------
  ModuleNotFoundError                       Traceback (most recent call last)
  &lt;ipython-input-4-d83b6b4f94f9&gt; in &lt;module&gt;
        1 get_ipython().system('pip install numpy')
  ----&gt; 2 import numpy as np
  
  ModuleNotFoundError: No module named 'numpy'
  </code></pre>
  <p>The package is already installed but still cannot be found...?</p>
  <p>Is there a way to fix this issue?</p>