How to do inheritance in python?

[tonilopezmr]

Could you show me a simple inheritance code in python?

Thanks you!!

[tonilopezmr]

@sergiotrujillomtz How can I do a utility class in python?

[srgtrujillo]

Hello @tonilopezmr, first I'll give you a brief explanation of inheritance in Python, doing a little comparison with the Java language.
As in the Java language, all objects inherit from the Object class. However there are some minor differences. In the Python language there is multiple inheritance and interfaces not exists as such. To achieve the same effect as Java interfaces, you can create classes that inherit from other abstract classes. You can find more information in https://docs.python.org/2.7/tutorial/classes.html#inheritance
This is a sample for simple inheritance:

class InterfaceClass(object):

    def do_something_1(self):
        raise NotImplementedError("Should have implemented this")

    def do_something_2(self):
        raise NotImplementedError("Should have implemented this")


class AbstractClass(InterfaceClass):

    def do_something_1(self):
        """
            Implementation
        """
        return 1

    def do_something_2(self):
        """
            Implementation
        """
        return 2

    def do_something_3(self):
        raise NotImplementedError("Should have implemented this")


class ConcreteClass(AbstractClass):

    def do_something_3(self):
        """
            Implementation
        """
        return 3

In response to your question,

How can I do a utility class in python?

what is usually done in Python is to create a module, which is not a class, it is a simple Python file containing all utility functions. Then you can import the module into any other implementation and use these functions. For example:
I have the package utility_module with 2 files; math_functions.py and __init__.py:

__init__.py:

from . import math_functions

math_functions.py:

def factorial(n):
    if not isinstance(n, int) or n < 0:
        raise ValueError("n is not integral or is negative")
    return n == 0 and 1 or n * factorial(n - 1)

def fibonacci(n):
    if not isinstance(n, int) or n < 0:
        raise ValueError("n is not integral or is negative")
    return 0 if n == 0 else 1 if n == 1 else fibonacci(n-1) + fibonacci(n-2)

Any implementation can import the module and use its functions. For example:

from utility_module import math_functions
from utility_module.math_functions import fibonacci

if __name__ == '__main__':
    print "7! = ", math_functions.factorial(7)
    print "fibonacci(8) = ", fibonacci(8)

You can find more information about Python modules and packages in https://docs.python.org/2/tutorial/modules.html

[tonilopezmr]

Thanks you very much!!!! 😍 😍

I hope that you continue writing more python code!

[tonilopezmr]

In AbstractClass, can I remove the method do_something_3?, because do_something_3 in InterfaceClass and AbstractClass is the same. 😊😊

[srgtrujillo]

If you remove the function do_something_3, AbstractClass will no longer be an abstract class. InterfaceClass does not contain the functinon do_something_3.

[tonilopezmr]

AHH yeah sorry! I didn't see that do_something_3 is a AbstractClass method.

But if you don't implement for example, do_something_2 in AbstractClass. Must you implement do_something_2 in ConcreteClass?