title: Multipart form-data POST using only default libraries?
body: <p>It would be great to get it done without any dependencies.<br>
  Here's how I'm currently doing it, but is not working:</p>
  
  <pre><code>data = urllib.parse.urlencode(
              {
                  'field':'value',
                  'field':'value',
                  'field':'value'
              }
          ).encode('utf-8')
  
  req = urllib.request.Request('http://www.example.com', data)
  
  response = opener.open(req).read().decode('utf-8')
  </code></pre>