Python3 Intermediate Level Topics

After going through the basics of python, you would be interested to know more about further and bit more advance topics of the Python3 programming language.
This article covers them.
Please remember that Python completely works on indentation and it is advised to practice it a bit by running some programs. Use the tab key to provide indentation to your code.

This article is divided in following five sections:

1. Classes
   Just like every other Object Oriented Programming language Python supports classes. Let’s look at some points on Python classes.
   • Classes are created by keyword class.
   • Attributes are the variables that belong to class.
   • Attributes are always public and can be accessed using dot (.) operator. Eg.: Myclass.Myattribute

   A sample E.g for classes:

   # creates a class named MyClass
   class MyClass:
           # assign the values to the MyClass attributes
           number = 0
           name = "noname"
   
   def Main():
           # Creating an object of the MyClass.
           # Here, 'me' is the object
           me = MyClass()
   
           # Accessing the attributes of MyClass
           # using the dot(.) operator
           me.number = 1337
           me.name = "Harssh"
   
           # str is an build-in function that
           # creates an string
           print(me.name + " " + str(me.number))
   
   # telling python that there is main in the program.
   if __name__=='__main__':
           Main()

   Output :

   Harssh 1337
   

2. Methods
   Method is a bunch of code that is intended to perform a particular task in your Python’s code.
   • Function that belongs to a class is called an Method.
   • All methods require ‘self’ parameter. If you have coded in other OOP language you can think of ‘self’ as the ‘this’ keyword which is used for the current object. It unhides the current instance variable.’self’ mostly work like ‘this’.
   • ‘def’ keyword is used to create a new method.

   # A Python program to demonstrate working of class
   # methods
   
   class Vector2D:
           x = 0.0
           y = 0.0
   
           # Creating a method named Set
           def Set(self, x, y):
                   self.x = x
                   self.y = y
   
   def Main():
           # vec is an object of class Vector2D
           vec = Vector2D()
   
           # Passing values to the function Set
           # by using dot(.) operator.
           vec.Set(5, 6)
           print("X: " + str(vec.x) + ", Y: " + str(vec.y))
   
   if __name__=='__main__':
           Main()

   Output :

   X: 5, Y: 6

3. Inheritance
   Inheritance is defined as a way in which a particular class inherits features from its base class.Base class is also knows as ‘Superclass’ and the class which inherits from the Superclass is knows as ‘Subclass’

   
   As shown in the figure the Derived class can inherit features from its base class, also it can define its own features too.

   # Syntax for inheritance
   
   class derived-classname(superclass-name)

   # A Python program to demonstrate working of inheritance
   class Pet:
           #__init__ is an constructor in Python
           def __init__(self, name, age):
                   self.name = name
                   self.age = age
   
   # Class Cat inheriting from the class Pet
   class Cat(Pet):
           def __init__(self, name, age):
                   # calling the super-class function __init__
                   # using the super() function
                   super().__init__(name, age)
   
   def Main():
           thePet = Pet("Pet", 1)
           jess = Cat("Jess", 3)
   
           # isinstance() function to check whether a class is
           # inherited from another class
           print("Is jess a cat? " +str(isinstance(jess, Cat)))
           print("Is jess a pet? " +str(isinstance(jess, Pet)))
           print("Is the pet a cat? "+str(isinstance(thePet, Cat)))
           print("Is thePet a Pet? " +str(isinstance(thePet, Pet)))
           print(jess.name)
   
   if __name__=='__main__':
           Main()

   Output :

   Is jess a cat? True
   Is jess a pet? True
   Is the pet a cat? False
   Is thePet a Pet? True
   Jess
   

4. Iterators
   Iterators are objects that can be iterated upon.
   • Python uses the __iter__() method to return an iterator object of the class.
   • The iterator object then uses the __next__() method to get the next item.
   • for loops stops when StopIteration Exception is raised.

   # This program will reverse the string that is passed
   # to it from the main function
   class Reverse:
       def __init__(self, data):
           self.data = data
           self.index = len(data)
   
       def __iter__(self):
           return self
   
       def __next__(self):
           if self.index == 0:
               raise StopIteration
           self.index-= 1
           return self.data[self.index]
   
   def Main():
       rev = Reverse('Drapsicle')
       for char in rev:
           print(char)
   
   if __name__=='__main__':
       Main()

   Output :

   e
   l
   c
   i
   s
   p
   a
   r
   D
   

5. Generators
   • Another way of creating iterators.
   • Uses a function rather than a separate class
   • Generates the background code for the next() and iter() methods
   • Uses a special statement called yield which saves the state of the generator and set a resume point for when next() is called again.

   # A Python program to demonstrate working of Generators
   def Reverse(data):
       # this is like counting from 100 to 1 by taking one(-1)
       # step backward.
       for index in range(len(data)-1, -1, -1):
           yield data[index]
   
   def Main():
       rev = Reverse('Harssh')
       for char in rev:
           print(char)
       data ='Harssh'
       print(list(data[i] for i in range(len(data)-1, -1, -1)))
   
   if __name__=="__main__":
       Main()

   Output :

   h
   s
   s
   r
   a
   H
   ['h', 's', 's', 'r', 'a', 'H']