title: Content-Length should be specified for iterable data of type <class 'dict'>
body: <pre><code>import urllib.request
  url = 'site'
  headers = {'Authorization' : 'Basic emVkMHg6WWJyYm5mMDA='}
  req = urllib.request.Request(url, headers)
  response = urllib.request.urlopen(req).getcode()
  </code></pre>
  
  <p>I wanted to write multi-threaded authorization on a remote server, but I see this:</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\Program Files\Python33\lib\urllib\request.py", line 1186, in do_request_
      mv = memoryview(data)
  TypeError: memoryview: dict object does not have the buffer interface
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "C:/Users/zed/Desktop/sddf.py", line 6, in &lt;module&gt;
      response = urllib.request.urlopen(req).getcode()
    File "C:\Program Files\Python33\lib\urllib\request.py", line 156, in urlopen
      return opener.open(url, data, timeout)
    File "C:\Program Files\Python33\lib\urllib\request.py", line 467, in open
      req = meth(req)
    File "C:\Program Files\Python33\lib\urllib\request.py", line 1191, in do_request_
      data))
  ValueError: Content-Length should be specified for iterable data of type &lt;class 'dict'&gt; {'Authorization': 'Basic emVkMHg6WWJyyM5mMDA='}
  </code></pre>