code: def open(self):
          
          try:
              connection = self.transport_class(
                  host=self.hostname,
                  username=self.username,
                  password=self.password,
                  timeout=self.timeout,
                  **self.eapi_kwargs
              )
  
              if self.device is None:
                  self.device = pyeapi.client.Node(connection, enablepwd=self.enablepwd)
              # does not raise an Exception if unusable
  
              # let's try to run a very simple command
              self.device.run_commands(["show clock"], encoding="text")
          except ConnectionError as ce:
              # and this is raised either if device not avaiable
              # either if HTTP(S) agent is not enabled
              # show management api http-commands
              raise ConnectionException(py23_compat.text_type(ce))
docs: Implementation of NAPALM method open.