title: Copying a file to an existing directory results in IOError [Error 21] is a directory
body: <p>I get this error:</p>
  
  <pre><code>IOError [Error 21] is a directory
  </code></pre>
  
  <p>when I try to copy a file to an existing directory. I do it like this:</p>
  
  <pre><code>shutil.copyfile(src, dst)
  </code></pre>
  
  <p>where <code>src</code> is a file and <code>dst</code> is an existing directory. What I'm doing wrong?</p>