title: error while using re.findall() to find all letters from A to Z
body: <p>My code is:</p>
  
  <pre><code>import re
  key, val = '  ', 2
    self._l[key] = re.findall(r"[A-Z]+", val)
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>return _compile(pattern, flags).findall(string)
  TypeError: expected string or bytes-like object
  </code></pre>