code: def user(self, login=None):
          
          if login:
              url = self._build_url('users', login)
          else:
              url = self._build_url('user')
  
          json = self._json(self._get(url), 200)
          return User(json, self._session) if json else None
docs: Returns a User object for the specified login name if
          provided. If no login name is provided, this will return a User
          object for the authenticated user.
  
          :param str login: (optional)
          :returns: :class:`User <github3.users.User>`