错误：尝试从 class 继承时出现“x 实例没有属性 y”

Question

I can't really understand what I'm doing wrong, since when I try it in "small scale" and it is working there.

I have a class named Play()

I goes like this:

class Play():
    def __init__(self):
        file = open("/home/trufa/Desktop/test", "r")
        self.word = random.choice(file.readlines()).rstrip()
        self.errAllowed = 7
        self.errMade = 0
        self.errList = []
        self.cheatsAllowed = 2##chetas not incrementing
        self.cheatsMade =0
        self.wordList = ["*"]*len(self.word) ##this one is the one I want to have available in another class

...

Then I have another class called Score()

class Score(Play):
    def __init__(self):
        self.initialScore = 0

    def letterGuess(self):
        self.initialScore += 1
        return self.errList

...

I instantiated both:

game = Play()
points = Score()

And if I do:

print points.letterGuess()

It gives me an error:

Traceback (most recent call last):
  File "/home/trufa/workspace/hangpy/src/v2.py", line 188, in <module>
    startGame()
  File "/home/trufa/workspace/hangpy/src/v2.py", line 134, in startGame
    print points.letterGuess()
  File "/home/trufa/workspace/hangpy/src/v2.py", line 79, in letterGuess
    return self.errList
AttributeError: Score instance has no attribute 'errList'

I don't understand why since I can do this without any trouble:

class One():
    def __init__(self):
        self.list= [1,2]

class Two(One):
    def meth(self):
        return self.list

uan = One()
tu = Two()

print uan.list 
print tu.meth() ## Both output [1,2]

I'm very new to OOP so I could be doing all kinds of silly mistakes but I can't figure out where!

I think I have posted all the relevant code, but I you think the error might be elsewhere, I can provide it.

^{As I said I'm very new, so this might have nothing to do with inheritance I just think it called that when you get "something" from within another class (you must be shouting at the screen by now)}

Answer 1

You overwrite the original __init__ , which is then never called and doesn't initialize the members. You must call the parent's __init__ separately, usually with this snippet:

def __init__(self):
    super(Score, self).__init__()

See the docs for super() for details. However, super() only works for so-called new-style classes. You must therefore either change the definition of Play to inherit from object :

class Play(object)

or you call the parent's method directly:

def __init__(self):
    Play.__init__(self)

Answer 2

When you inherit from the class Play , you automatically get the attributes that you've created in the definition of Play , but you don't get the attributes that you've created in Play.__init__ . You have to explicitly call it like so:

class Score(Play):
    def __init__(self):
        Play.__init__(self)
        self.initialScore = 0

See Boldewyn's suggestion for using super to do this; but IMO you should probably get used to the basic way inheritance works before fiddling with super .

To further clarify, if you don't override __init__ as you have in this case, then it's inherited and called automatically.

Answer 3

You forgot to initialize the superclass.

class Score(Play):
  def __init__(self):
    super(Score, self).__init__()
    self.initialScore = 0