title: Explaining advanced string formatting python
body: <p>I'm trying to understand how <a href="https://codegolf.stackexchange.com/a/193447">this answer on Code Golf</a> works, turning integers into french licence plates with the following code:</p>
  
  <pre><code>lambda n:f"%c%c-{n%1000:03}-%c%c"%(*(65+n//1000//26**i%26for i in[3,2,1,0]),)
  </code></pre>
  
  <p>I understand <code>'%c'</code> with <code>65 + n</code> on a <code>% 26</code> number to get the letters, and I understand <code>% 1000 : 03</code> for getting <code>3-0</code> padded numbers up to <code>999</code>. However I can't find anything on the following:</p>
  
  <ul>
  <li>the use of two forward slashes here</li>
  <li>the effect of the <code>{ }</code> brackets in the string</li>
  </ul>
  
  <p>Explanations would be much appreciated - thanks!</p>