title: r.headers['Authorization'] in python2.7 class's __call__ function
body: <p>I'm digging a little into requests/requests/auth.py file at master kennethreitz/requests on github. </p>
  
  <p><a href="https://github.com/kennethreitz/requests/blob/master/requests/auth.py" rel="nofollow">https://github.com/kennethreitz/requests/blob/master/requests/auth.py</a></p>
  
  <p>And I saw this code, </p>
  
  <pre><code>class HTTPBasicAuth(AuthBase):
  """Attaches HTTP Basic Authentication to the given Request object."""
  def __init__(self, username, password):
      self.username = username
      self.password = password
  
  def __call__(self, r):
      r.headers['Authorization'] = _basic_auth_str(self.username, self.password)
      return r
  </code></pre>
  
  <p>I just can't understand how could he comes up with r.headerp['Authorisation '] which hasn't been defined anywhere before. Am I missing something?</p>
  
  <p>Many thanks for someone to answer the problem :)</p>