在Python中使用self内部实例方法

Question

I have a class like this

class Test:
    def __init__(self, var):
        self.var = var
    def test(self):
        x = self.var + 2
        return x

And then I make a class like this

class Test:
    def __init__(self, var):
        self.var = var
    def test(self):
        self.x = self.var + 2
        return self.x

I understand that I can use self to separate attribute values across various instances of this class. My question is, if I create many utility variables (like x ) inside a method, should I always create them using self ?

Can anyone explain how the above two classes behave differently (if they do)?

Answer 1

Let's see the difference between the two classes :

class Test:
    def __init__(self, var):
        self.var = var
    def test(self):
        x = self.var + 2
        return x

Let's create a Test object:

t = Test(1)

And see what we can do

t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # Still erroring

And with your second class

class Test:
    def __init__(self, var):
        self.var = var
    def test(self):
        self.x = self.var + 2
        return self.x

Let's create a Test object:

t = Test(1)

And see what we can do

t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # 3

So what ? Well we can see that any variables defined with self.VARNAME persist in the instance, while simple local variables, without self. , dosen't.

However, if x needs to be accessible with tx, i'd probably go for a property, like so

class Test:
    def __init__(self, var):
        self.var = var

    @property
    def x(self):
        x = self.var + 2
        return x

t = Test() 
t.x # 3