How to use the problog.engine.DefaultEngine function in problog

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

#! /usr/bin/env python3

from problog.program import PrologString
from problog.engine  import DefaultEngine
from problog.logic   import Constant,Term,And,Clause
from problog         import get_evaluatable

import time
import math
import inspect

class MDPProbLog():
	_eng = DefaultEngine(label_all=True)

	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