title: Python does not finding installed library
body: <p>I have recently come across to this error: </p>
  
  <pre class="lang-none prettyprint-override"><code>~/Works/PolymerAnimation/PDF_try » python3 slope.py                                                       marco@MPB-2^Q5Ghz-16Gb
  Traceback (most recent call last):
    File "slope.py", line 4, in &lt;module&gt;
      import numpy as np
  ModuleNotFoundError: No module named 'numpy'
  ---------------------------------------------------------------------------------------------------------------------------------
  ~/Works/PolymerAnimation/PDF_try » pip3 install numpy                                                     marco@MPB-2^Q5Ghz-16Gb
  Requirement already satisfied: numpy in /usr/local/lib/python3.7/site-packages (1.18.0)
  </code></pre>
  
  <p>I have a 2012 macbook pro and since today I never have problem using python, I have also installed numpy using homebrew (package manager for mac) ... I don't know what's going on! Numpy is not a unique module that is give me this problem ... but all the module .. like matplotlib and so on! </p>