Overriding part of the __init__ method in a subclass in Python 2

I'm wanting to create a subclass of a subclass (Barrier is a type of wall, which is a type of obstacle), and I'm wanting the barrier to have the same init method as wall with the exception that the self.type = 'barrier', but I'm not sure how to do this (I'm very new to programming so I'm sorry if this is very simple but I haven't been able to find an answer I understand). So far I have:

class Obstacle:
    def __init__(self, type):
        self.type = 'obstacle'

    def __str__(self):
        return "obstacle"

class Wall(Obstacle):

    def __init__(self, origin, end):

        self.type = 'wall'
        self.origin = origin
        self.end = end

        # etc.... (i.e. there are more things included in here which the 
        # that the barrier also needs to have (like coordinate vectors etc.)

class Barrier(Wall):

    def __str__(self):
        return "Barrier obstacle"

How do I change it so that class Barrier has identical contents of the init method as Walls do, except their "self.type = 'barrier'"?