Misunderstanding over classes and definitions

Question

I have been given these two class definitions:

class Weird(object):
    def __init__(self, x, y): 
        self.y = y
        self.x = x
    def getX(self):
        return x 
    def getY(self):
        return y

class Wild(object):
    def __init__(self, x, y): 
        self.y = y
        self.x = x
    def getX(self):
        return self.x 
    def getY(self):
        return self.y

X = 7
Y = 8

The first two questions were fine; they simply asked

w2 = Wild(X, Y)
print(w2.getX())

(which is 7) and

print(w2.getY())

What confuses me are the questions

w1 = Weird(X, Y)
print(w1.getX())

and

print(w1.getY())

both of whose answers are apparently "error", but I don't understand why this is the case. The errors given are "x is not defined" and "y is not defined" respectively, but I thought x and y are the parameters that we put into the function. What am I missing?

`x` and `y` are locals in `Weird.__init__`. That means they don't exist *outside* of that function. `Weird.getX` and `Weird.getY` are separate functions with separate namespaces. — Martijn Pieters, Apr 15 '17 at 14:48
`Wild` uses the `self` object (a reference to your current instance) to access attributes on that. That's how you share information between the different methods, they all share a `self` instance, which is passed in automatically for methods. `self.x` and `self.y` exist only because `__init__` set these. — Martijn Pieters, Apr 15 '17 at 14:49
@alexqwx: you want to look up what *attributes* are then. The obvious difference is the `self.` part there. — Martijn Pieters, Apr 15 '17 at 14:50
See [Why do you need "self." in Python to refer to instance variables?](//softwareengineering.stackexchange.com/q/303082) — Martijn Pieters, Apr 15 '17 at 14:51
Also https://pythontips.com/2013/08/07/the-self-variable-in-python-explained/, and many other posts. — Martijn Pieters, Apr 15 '17 at 14:52
Last but not least, the Python tutorial: https://docs.python.org/3/tutorial/classes.html — Martijn Pieters, Apr 15 '17 at 14:56

score 0 · Accepted Answer · answered Apr 15 '17 at 14:53

0

In your first class, x and y are constructor arguments. They are not accessible out of this scope.

In the getX function, x doesn't exists. You need to retrieve it from the self reference, such as in your second class.

answered Apr 15 '17 at 14:53

Kmaschta

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Misunderstanding over classes and definitions

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