E319: Sorry, the command is not available in this version on macvim
It may be because you do not have the correct clang-format.py file downloaded. If vim is compiled using python3 then you need a different file because it is in python2. I downloaded a new python file and changed the key mapping recommended by in the clang python file to the following in my .vimrc: 

    map &lt;C-I&gt; :py3file &lt;path-to-this-file&gt;/clang-format.py&lt;cr&gt;
    imap &lt;C-I&gt; &lt;c-o&gt;:py3file &lt;path-to-this-file&gt;/clang-format.py&lt;cr&gt;


This solved the E319 problem I was getting.