# 02-Python Cont.

###### tags: `GENERAL`

# Class and Object

A class is a blueprint for the object.

class Parrot:
    pass

An object (instance) is an instantiation of a class. When class is defined, only the description for the object is defined. Therefore, no memory or storage is allocated.

obj = Parrot()

Here, obj is an object of class Parrot.

class Parrot:

    # class attribute
    species = "bird"

    # instance attribute
    def __init__(self, name, age):
        self.name = name
        self.age = age

# instantiate the Parrot class
blu = Parrot("Blu", 10)
woo = Parrot("Woo", 15)

# access the class attributes
print("Blu is a {}".format(blu.__class__.species))
print("Woo is also a {}".format(woo.__class__.species))

# access the instance attributes
print("{} is {} years old".format( blu.name, blu.age))
print("{} is {} years old".format( woo.name, woo.age))

Output

Blu is a bird
Woo is also a bird
Blu is 10 years old
Woo is 15 years old

## Methods

Methods are functions defined inside the body of a class. They are used to define the behaviors of an object.

class Parrot:
    
    # instance attributes
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    # instance method
    def sing(self, song):
        return "{} sings {}".format(self.name, song)

    def dance(self):
        return "{} is now dancing".format(self.name)

# instantiate the object
blu = Parrot("Blu", 10)

# call our instance methods
print(blu.sing("'Happy'"))
print(blu.dance())

Output

Blu sings 'Happy'
Blu is now dancing

## Inheritance

Inheritance is a way of creating a new class for using details of an existing class without modifying it. The newly formed class is a derived class (or child class). Similarly, the existing class is a base class (or parent class).

# parent class
class Bird:
    
    def __init__(self):
        print("Bird is ready")

    def whois_this(self):
        print("Bird")

    def swim(self):
        print("Swim faster")

# child class
class Penguin(Bird):

    def __init__(self):
        # call super() function
        super().__init__()
        print("Penguin is ready")

    def whois_this(self):
        print("Penguin")

    def run(self):
        print("Run faster")

peggy = Penguin()
peggy.whois_this()
peggy.swim()
peggy.run()

Output

Bird is ready
Penguin is ready
Penguin
Swim faster
Run faster

# File operations and context managemnet

## File operations

Opening Files in Python

Python has a built-in open() function to open a file. This function returns a file object, also called a handle, as it is used to read or modify the file accordingly.

f = open("test.txt")    # open file in current directory
f = open("C:/Python38/README.txt")  # specifying full path

f = open("test.txt")      # equivalent to 'r' or 'rt'
f = open("test.txt",'w')  # write in text mode
f = open("img.bmp",'r+b') # read and write in binary mode

f = open("test.txt", encoding = 'utf-8')
# perform file operations
f.close()

try:
   f = open("test.txt", encoding = 'utf-8')
   # perform file operations
except Error as e:
    print('error occured')
finally:
   f.close()

## context management

with open("test.txt", encoding = 'utf-8') as f:
   # perform file operations

with open("test.txt",'w',encoding = 'utf-8') as f:
   f.write("my first file\n")
   f.write("This file\n\n")
   f.write("contains three lines\n")

# Modules

# Task