title: Return a Boolean if a string consists of a hex character
body: <p>I want to know if a string is using an escape character to represent a hex character. Something that works in the same style as <code>string.isalnum()</code>:</p>
  
  <pre><code>"\x01".ishex()
  </code></pre>
  
  <p>returns <code>True</code></p>
  
  <p>and</p>
  
  <pre><code>"^".ishex()
  </code></pre>
  
  <p>returns <code>False</code>.</p>
  
  <p>Does such a function exist?</p>
  
  <p>If not, is there anything that returns <code>True</code> if it only contains escape characters?</p>