How to use the problog.program.PrologString function in problog

def __init__(self, program):
        self._engine = DefaultEngine()
        self._db = self._engine.prepare(PrologString(program))
        self._gp = None
        self._knowledge = None

def __init__(self, model, gamma, epsilon):
		self._model = model
		self._gamma = gamma
		self._epsilon = epsilon

		print("  >> Preprocessing program ...", end=" ")
		start = time.clock()
		self._db = self._eng.prepare(PrologString(model))
		self._build_state_atoms()
		self._get_action_atoms()
		self._build_action_rules()
		self._build_value_function_rules()
		self._utilities = dict(self._eng.query(self._db, Term('utility', None, None)))
		end = time.clock()
		uptime = end-start
		print("Done in {0:.3f}sec.".format(uptime))

		print("  >> Relevant grounding ...", end=" ")
		start = time.clock()
		self._gp = self._eng.ground_all(self._db, target=None, queries=self._utilities.keys())
		end = time.clock()
		uptime = end-start
		print("Done in {0:.3f}sec.".format(uptime))

def solve_problog(model, debug=False):
    program = PrologString(model)
    decisions, score, statistics = dtproblog(program)
    if debug:
        print('score: %s' % score)
        for name, value in decisions.items():
            print('%s: %s' % (name, value))
    return (score, decisions)