from random  import choice
class RandomWalk():
    def _init_(self,num_points=5000):
        self.num_points=num_points
        self.x_values=[0]
        self.y_values=[0]
    def fill_walk(self):
        while len(self.x_values)<self.num_points:


            x_direction=choice([1,-1])
            x_distance=choice([0,1,2,3,4])
            x_step=x_direction * x_distance
            y_direction=choice([1,-1])
            y_distance=choice([0,1,2,3,4])
            y_step=y_direction * y_distance
            if x_step==0 and y_step==0:
                continue
            next_x=self.x_values[-1]+x_step
            next_y=self.y_values[-1]+y_step
            self.x_values.append(next_x)
            self.y_values.append(next_y)



Traceback (most recent call last):
  File "rw_visual.py", line 4, in <module>
    rw.fill_walk()
  File "E:\python_work\random_walk.py", line 8, in fill_walk
    while len(self.x_values)<self.num_points:
AttributeError: 'RandomWalk' object has no attribute 'x_values'

------------------
(program exited with code: 1)
请按任意键继续. . .


求大神解答 ，这个问题怎么解决？