How to call Base Class's __init__ method from the child class?

PythonPython 2.7InheritanceConstructor

Python Problem Overview


If I have a python class as:

class BaseClass(object):
#code and the init function of the base class

And then I define a child class such as:

class ChildClass(BaseClass):
#here I want to call the init function of the base class

If the init function of the base class takes some arguments that I am taking them as arguments of the child class's init function, how do I pass these arguments to the base class?

The code that I have written is:

class Car(object):
    condition = "new"

    def __init__(self, model, color, mpg):
        self.model = model
        self.color = color
        self.mpg   = mpg

class ElectricCar(Car):
    def __init__(self, battery_type, model, color, mpg):
        self.battery_type=battery_type
        super(ElectricCar, self).__init__(model, color, mpg)

Where am I going wrong?

Python Solutions


Solution 1 - Python

You could use super(ChildClass, self).__init__()

class BaseClass(object):
    def __init__(self, *args, **kwargs):
        pass

class ChildClass(BaseClass):
    def __init__(self, *args, **kwargs):
        super(ChildClass, self).__init__(*args, **kwargs)

Your indentation is incorrect, here's the modified code:

class Car(object):
    condition = "new"

    def __init__(self, model, color, mpg):
        self.model = model
        self.color = color
        self.mpg   = mpg

class ElectricCar(Car):
    def __init__(self, battery_type, model, color, mpg):
        self.battery_type=battery_type
        super(ElectricCar, self).__init__(model, color, mpg)

car = ElectricCar('battery', 'ford', 'golden', 10)
print car.__dict__

Here's the output:

{'color': 'golden', 'mpg': 10, 'model': 'ford', 'battery_type': 'battery'}

Solution 2 - Python

As Mingyu pointed out, there is a problem in formatting. Other than that, I would strongly recommend not using the Derived class's name while calling super() since it makes your code inflexible (code maintenance and inheritance issues). In Python 3, Use super().__init__ instead. Here is the code after incorporating these changes :

class Car(object):
    condition = "new"

    def __init__(self, model, color, mpg):
        self.model = model
        self.color = color
        self.mpg   = mpg

class ElectricCar(Car):

    def __init__(self, battery_type, model, color, mpg):
        self.battery_type=battery_type
        super().__init__(model, color, mpg)

Thanks to Erwin Mayer for pointing out the issue in using __class__ with super()

Solution 3 - Python

If you are using Python 3, it is recommended to simply call super() without any argument:

class Car(object):
    condition = "new"

    def __init__(self, model, color, mpg):
        self.model = model
        self.color = color
        self.mpg   = mpg

class ElectricCar(Car):
    def __init__(self, battery_type, model, color, mpg):
        self.battery_type=battery_type
        super().__init__(model, color, mpg)

car = ElectricCar('battery', 'ford', 'golden', 10)
print car.__dict__

Do not call super with class as it may lead to infinite recursion exceptions as per [this answer][1]. [1]: https://stackoverflow.com/a/19776143/541420

Solution 4 - Python

You can call the super class's constructor like this

class A(object):
	def __init__(self, number):
		print "parent", number

class B(A):
	def __init__(self):
		super(B, self).__init__(5)

b = B()

NOTE:

This will work only when the parent class inherits object

Attributions

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Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionpraxmonView Question on Stackoverflow
Solution 1 - PythonMingyuView Answer on Stackoverflow
Solution 2 - PythonManjunath ReddyView Answer on Stackoverflow
Solution 3 - PythonErwin MayerView Answer on Stackoverflow
Solution 4 - PythonthefourtheyeView Answer on Stackoverflow