21 - inheritance.py

# Python inheritance
"""Inheritance allows us to define a class that inherits all the methods and properties 
from another class.

Parent class is the class being inherited from, also called base class.

Child class is the class that inherits from another class, also called derived class"""
# Create a parent class


class Person:
    def __init__(self, fname, lname):
        self.firstname = fname
        self.lastname = lname

    def printname(self):
        print(self.firstname, self.lastname)


# Use the Person class to create an object, and then execute the printname method:
x = Person("John", "Doe")
x.printname()

# Create a child class


class Student(Person):
    pass


# Example
x = Student("Mike", "Olsen")
x.printname()

"""When you add the __init__() function, the child class will no longer inherit 
the parent's __init__() function.

To keep the inheritance of the parent's __init__() function, add a call to the 
parent's __init__() function:
"""


class Student(Person):
    def __init__(self, fname, lname):
        Person.__init__(self, fname, lname)


# Using the super() function
"""Python also has a super() function that will make the child class inherit 
all the methods and properties from its parent"""


class Student(Person):
    def __init__(self, fname, lname):
        super().__init__(fname, lname)


# Add properties
"""In the example below, the year 2019 should be a variable, and passed into the Student class 
when creating student objects. To do so, add another parameter in the __init__() function"""


class Student(Person):
    def __init__(self, fname, lname, year):
        super().__init__(fname, lname)
        self.graduationyear = year


x = Student("Mike", "Olsen", 2019)

# Add methods


class Student(Person):
    def __init__(self, fname, lname, year):
        super().__init__(fname, lname)
        self.graduationyear = year

    def welcome(self):
        print("Welcome", self.firstname, self.lastname,
              "to the class of", self.graduationyear)