2个文件中的Python类[艰苦学习Python]

Question

Hey guys, I'm currently completing Zed Shaw's "Learn Python the Hard Way" and I've been struggling with Exercise 43, which instructs the learner to make a game. For simplicity, I am attempting to rewrite the previous exercise that has a class Game and some functions:
__init__ , play , death , and four more for each "room" in the game.

I was able to copy and modify the code for various conditions, but I wanted to try to split the code in to two files: one file containing a class PrincessRoom to be the sole room for the game, and the other containing the bulk of the old code play and death .

From ex43.py

from sys import exit
from random import randint
from ex43princess import PrincessRoom

class Game(object):

    def __init__(self, start):
        self.quips = [
            "You died. You suck.",
            "Hey, you died. Look at that.",
            "You lose. I win. End.",
        ]
        self.start = start

    def play(self):
        next = self.start

        while True:
            print "\n--------"
            room = getattr(self, next)
            next = room()

    def death(self):
        print self.quips[randint(0, len(self.quips)-1)]
        exit(1)

a_game = Game("princess")
a_game.play()

From ex43princess.py

class PrincessRoom(object):

    def __init__(self):
        pass

    def princess(self):
        print "text here"

        raw_input("> ")

        if raw_input == 1:
            return 'eat_it'
        else:
            return 'death'

    def eat_it(self):
        print "text here"

When I run the code, here's the error I get:

Traceback (most recent call last):
  File "ex43-2.py", line 29, in <module>
    a_game.play()
  File "ex43-2.py", line 21, in play
    room = getattr(self, next)
AttributeError: 'Game' object has no attribute 'princess'``

Now I'm not too solid on why the original code had a_game initialized with a_game = Game("princess") but I'm pretty sure it's directly related to why it has me use room = getattr(self, next) . But this is where my understanding falters.

If memory serves, it would appear that Game object isn't inheriting properly from ex43princess.py... right?

If any one could help me understand what is happening here I would be much appreciative.

Thanks! Josh

Answer 1

Note: I'm not familiar with the book and hence with the context of the question, so my answer refers to the displayed code only

The problem here isn't splitting the code to two files. As far as I can see, the PrincessRoom class in its own file presents no real problem.

Game can't find the princess method, and it doesn't have one. Perhaps it should've inherited from PrincessRoom ?

That said, I'm not sure that it makes sense logically to inherit a class named Game from a class named PrincessRoom . A better approach IMHO would be aggregation - ie keep a collection of rooms as an instance variable of Game and access them through it. Inheritance should be really reserved to is-a relations. You should ask yourself, whether "Game is-a PrincessRoom" makes sense. It probably doesn't. What does make sense is "Game has-a PrincessRoom", and has-a is represented by aggregation in OOP.

Answer 2

My quick and dirty version of exercise 43. Here . The key is that you are just trying to instantiate the PrincessRoom objects but you can't do it with just a string like you are trying to do.