title: Upgrading Python 3.7 to 3.9 on macOS Big Sur
body: <p>I'm trying to upgrade Python 3.7 to 3.9 on macOS Big Sur. I'm also trying to avoid losing packages that were installed on Python 3.7 and reinstalling them again on Python 3.9</p>
  <p>I tried using</p>
  <pre><code>brew install python3
  brew update &amp;&amp; brew upgrade python
  </code></pre>
  <p>which yielded</p>
  <pre><code>Already up-to-date.
  Warning: python3 3.9.1_7 already installed
  </code></pre>
  <p>However when I run <code>python3 --version</code> it yields <code>Python 3.7.0</code></p>
  <p>Is this an issue with the alias? Is there a way to uninstall Python 3.7 and keep Python 3.9?</p>
  <p>Running <code>brew link python3</code> yields</p>
  <pre><code>Linking /usr/local/Cellar/python@3.9/3.9.1_7... 
  Error: Could not symlink bin/2to3
  Target /usr/local/bin/2to3
  already exists. You may want to remove it:
    rm '/usr/local/bin/2to3'
  
  To force the link and overwrite all conflicting files:
    brew link --overwrite python@3.9
  
  To list all files that would be deleted:
    brew link --overwrite --dry-run python@3.9
  </code></pre>