title: AttributeError: 'dict' object has no attribute 'encode'
body: <p>I'm trying to post a request to the target website using multi part form data </p>
  
  <pre class="lang-py prettyprint-override"><code>m = MultipartEncoder(
      fields={"auth":{"id":str(random.randint(0, 999991)),"sign":randoms(32)},
      "data":{"action":"login","login":"embrella","password":"steffano321","stayLogged":"False"}
      })
  s = requests.Session()
  s.post('targetwebsite', data=m, headers=headers['Content-Type': m.content_type], timeout=5)
  </code></pre>
  
  <p>But I always end up with</p>
  
  <pre><code>line 25, in &lt;module&gt;
      "data":{"action":"login","login":"embrella","password":"steffano321","stayLogged":"False"}
  AttributeError: 'dict' object has no attribute 'encode'
  </code></pre>
  
  <p>I don't know what's causing this, I've even tried converting to JSON first then posting</p>
  
  <pre class="lang-py prettyprint-override"><code>uuhh = {'auth':{"id":str(random.randint(0, 999991)),"sign":randoms(32)},
      "data":{"action":"login","login":"embrella","password":"steffano321","stayLogged":"False"}}
      fields = json.dumps(uuhh)
  m = MultipartEncoder(fields=fields)
  </code></pre>
  
  <p>But it says <code>ValueError: not enough values to unpack (expected 2, got 1)</code> so I guess that is very wrong.</p>