Python inherit variables from parent class

Question

Sorry if I don't explain it that well but I'll try my best:

So I want to inherit the variables from the Parent class, but I don't want to pass them again when creating an instance of the Child class because I think that is redundant. I just want to use the eye color from the Parent for example. See the example code below for what I mean

This is what works:

class Parent:
    def __init__(self, eye_color, length):
        self.eye_color = str(eye_color)
        self.length = length


class Child(Parent):
    def __init__(self, gender, eye_color, length):
        super().__init__(eye_color, length)
        self.gender = str(gender)

x = Parent("Blue", 2)
y = Child("Men", "Blue", 2)

print(x.eye_color, x.length)
print(y.gender, x.length)

This is what I somehow want:

class Parent:
    def __init__(self, eye_color, length):
        self.eye_color = str(eye_color)
        self.length = length


class Child(Parent):
    def __init__(self, gender):
        super().__init__(eye_color, length)
        self.gender = str(gender)

x = Parent("Blue", 2)
y = Child("Men")

print(x.length, x.eye_color)
print(y.gender, x.length)

You can't get what you want. But you can use *args, **kwargs to almost get there. — wim
– wim, Commented Mar 2, 2017 at 16:47
eye_color and length are specific to an instance of Parent, not the class as a whole. Given x1 = Parent("Blue", 2), x2 = Parent("Green", 3), and y = Child("Men"), what should the value of y.eye_color or y.length be? At the very least, Child.__init__ would need to take a Parent instance as an argument. — chepner
– chepner, Commented Mar 2, 2017 at 16:47
You can create a create_child method in Parent class that will return an instance of Child class with parent characteristics. So you can use it like y = x.create_child() — Vitalii Strimbanu
– Vitalii Strimbanu, Commented Mar 2, 2017 at 16:49

lelabo_m · Accepted Answer · 2019-03-18 17:29:22Z

4

What you ask does not make sense:

class Parent:
    def __init__(self, eye_color, length):
        self.eye_color = str(eye_color)
        self.length = length


class Child(Parent):
    def __init__(self, gender):
        super().__init__(eye_color, length)
        self.gender = str(gender)

x = Parent("Blue", 2)
y = Child("Men")

print(x.length, x.eye_color)
print(y.gender, x.length)

In child, the parameters eye_color and length come from nowhere.

rassar example is good if you want to reuse a parent object.

You can also do the following:

class Parent:
    # def __init__(self, eye_color=(default value here), length=(default value here)):
    def __init__(self, eye_color="", length=0):
        self.eye_color = str(eye_color)
        self.length = length

OR

class Parent:
    def __init__(self, eye_color="", length=0):
        self.eye_color = str(eye_color)
        self.length = length

class Child(Parent):
    def __init__(self, gender, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.gender = str(gender)

x = Parent("Blue", 2)
y = Child("Men") # Work with first example of Parent
y = Child("Men", eye_color="Blue", length=2) # Work with first
y = Child("Men", "Blue", 2) # Work with second example

print(x.length, x.eye_color)
print(y.gender, y.length)

edited Mar 18, 2019 at 17:29

answered Mar 2, 2017 at 17:01

lelabo_m

5098 silver badges21 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

stickfigure4 Over a year ago

Thank you this is really helpful, but I think rassar solution is a better approach for me, anyway I'll try coding and see what's best to use.

ApplePie Over a year ago

To be fair, maybe OP's question does not make sense but I found this page looking exactly for this solution because this is something inheritance in C++ will do.

lelabo_m Over a year ago

Sorry, I did not mean the question was stupid, just that the example of what it was trying to do in python made no sense because some variables were not passed through.

rassar · Accepted Answer · 2017-03-03 15:32:36Z

2

You could try passing a Parent instance to the Child initializer...That's probably the closest you'll get.

class Parent:
    def __init__(self, eye_color, length):
        self.eye_color = str(eye_color)
        self.length = length


class Child(Parent):
    def __init__(self, gender, parent):
        super().__init__(parent.eye_color, parent.length)
        self.gender = str(gender)

x = Parent("Blue", 2)
y = Child("Men", x)

print(x.length, x.eye_color)
print(y.gender, x.length)

Another thing you could do is hold a last_parent variable:

global last_parent

class Parent:
        def __init__(self, eye_color, length):
            self.eye_color = str(eye_color)
            self.length = length
            last_parent = self


class Child(Parent):
    def __init__(self, gender):
        super().__init__(last_parent.eye_color, last_parent.length)
        self.gender = str(gender)

x = Parent("Blue", 2)
y = Child("Men")

print(x.length, x.eye_color)
print(y.gender, x.length)

edited Mar 3, 2017 at 15:32

answered Mar 2, 2017 at 16:53

rassar

5,7103 gold badges29 silver badges46 bronze badges

1 Comment

stickfigure4 Over a year ago

Thanks your solution is very helpful! I think I'll go with this approach.

Collectives™ on Stack Overflow

Python inherit variables from parent class

2 Answers 2

3 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related