title: Why are python modules not found despite installing them in pip?
body: <p>I've been trying to use VS Code's python debugger on Linux (mint), which uses debugpy and it keeps giving the error &quot;No module named '_ctypes'&quot;. Installing libffi-dev didn't fix it as suggested elsewhere on SO and neither did reinstalling python and python3; so, I tried installing debugpy through pip:</p>
  <p><code>pip install debugpy</code></p>
  <p>Which installs with no issues. However, both <code>python</code> and <code>python3</code> commands cannot find the module despite the fact that the module is installed (which I can see when I enter <code>pip list</code>)</p>
  <pre><code>python -m debugpy
  /usr/bin/python: No module named debugpy
  </code></pre>
  <pre><code>python3 -m debugpy
  /usr/local/bin/python3: No module named debugpy
  </code></pre>
  <p>So after trying to reinstall pip multiple times, I tried installing through the pip module</p>
  <pre><code>python -m pip install debugpy
  /usr/bin/python: No module named pip
  </code></pre>
  <pre><code>python3 -m pip install debugpy
  /usr/local/bin/python3: No module named pip
  </code></pre>
  <p>So it seems my pip module is also missing too. It may have something to do with my multiple installations of python3 as it seems that there is one in <strong>/bin</strong> and in <strong>/usr/local/bin</strong> and the local installation is the one that gets called with the python3 command according to <code>which python3</code>.
  This leads to multiple questions:</p>
  <ol>
  <li>Should the pip module be installed in python, and if so how do I install it again?</li>
  <li>How can I get the pip command to actually install the modules into python?</li>
  <li>How can I ensure that there is only one python3 installation in Linux (mint/ubuntu)?</li>
  </ol>
  <p>Thank-you. If it helps answer the question, I do not seem to have a <code>PYTHONPATH</code> variable.</p>