title: macos big sur - brew install python@2 doesnt work after uninstall python@2
body: <p>after I tried to uninstall python 2.7</p>
  <pre><code>% brew uninstall python@2     
  </code></pre>
  <p>I cannot reinstall back python 2.7 on my mac (big sur)</p>
  <pre><code>% brew install python@2                                    
  Error: 
    homebrew-core is a shallow clone.
    homebrew-cask is a shallow clone.
  To `brew update`, first run:
    git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow
    git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask fetch --unshallow
  This restriction has been made on GitHub's request because updating shallow
  clones is an extremely expensive operation due to the tree layout and traffic of
  Homebrew/homebrew-core and Homebrew/homebrew-cask. We don't do this for you
  automatically to avoid repeatedly performing an expensive unshallow operation in
  CI systems (which should instead be fixed to not use shallow clones). Sorry for
  the inconvenience!
  ==&gt; Searching for similarly named formulae...
  Error: No similarly named formulae found.
  Error: No available formula or cask with the name &quot;python@2&quot;.
  ==&gt; Searching for a previously deleted formula (in the last month)...
  Warning: homebrew/core is shallow clone. To get complete history run:
    git -C &quot;$(brew --repo homebrew/core)&quot; fetch --unshallow
  
  Error: No previously deleted formula found.
  ==&gt; Searching taps on GitHub...
  Error: No formulae found in taps.
  </code></pre>
  <p>UPDATE: I notice this as well</p>
  <pre><code>% pwd
  /Library/Frameworks/Python.framework/Versions
  % ls -al
  total 0
  drwxrwxr-x   6 root  wheel  192 Jan 11 14:18 .
  drwxr-xr-x   6 root  wheel  192 Jan 11 14:18 ..
  drwxrwxr-x  10 root  admin  320 Nov  8  2017 3.6
  drwxrwxr-x  10 root  admin  320 Jan  2 18:24 3.8
  drwxrwxr-x  11 root  admin  352 Jan 11 14:18 3.9
  lrwxr-xr-x   1 root  wheel    3 Jan 11 14:18 Current -&gt; 3.9
  % python -V  
  Python 2.7.16
  % python3 -V
  Python 3.9.1
  
  in another location
  
  % ls -al
  total 0
  drwxr-xr-x   7 root  wheel  224 Jan  1  2020 .
  drwxr-xr-x   5 root  wheel  160 Jan  1  2020 ..
  lrwxr-xr-x   1 root  wheel    3 Jan  1  2020 2.3 -&gt; 2.7
  lrwxr-xr-x   1 root  wheel    3 Jan  1  2020 2.5 -&gt; 2.7
  lrwxr-xr-x   1 root  wheel    3 Jan  1  2020 2.6 -&gt; 2.7
  drwxr-xr-x  11 root  wheel  352 Jan  1  2020 2.7
  lrwxr-xr-x   1 root  wheel    3 Jan  1  2020 Current -&gt; 2.7
  % pwd
  /System/Library/Frameworks/Python.framework/Versions
  </code></pre>
  <p>There seems to be 2 installed locations for python in Mac</p>
  <pre><code>/Library/Frameworks/Python.framework/Versions
  /System/Library/Frameworks/Python.framework/Versions
  </code></pre>
  <p>How can I reinstall python 2.7 or say reinstate it if its unlinked ?</p>