class_docstr: SumoTLManager is responsible for the management of the sumo traffic lights (i.e., keeps control
  of the current program, phase, ...)
class_docstr_tok: ["SumoTLManager","is","responsible","for","the","management","of","the","sumo","traffic","lights","(","i.e.",",","keeps","control","of","the","current","program",",","phase",",","...",")"]
docstr: Returns all the traffic light signals.
docstr_tok: ["Returns","all","the","traffic","light","signals","."]
code: def get_all_signals(self):
      """
      Returns all the traffic light signals.
      """
      signals = set()
      for tlid, program_id in self._current_program.items():
          signals.update(self._tls[tlid][program_id].get_all_signals())
      return signals
  
imports: import collections
  import enum
  import logging
  import os
  import carla
  import sumolib
  import traci
  from .constants import INVALID_ACTOR_ID
  import lxml.etree
label_desc: Use image node_id 4 for calling the SumoTLManager obj's underlying member method code with example usage: obj.get_all_signals() and returns: signals