Classes and Objects
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Classes & Objects
Part 1
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Classes
A class is a programmer defined type.
Classes can be thought of as a blueprint for creating objects.
class Car:
"""Represents a wheeled motor vehicle used for transportation."""
pass
Car
# <class '__main__.Car'>
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Objects
To create a car, you call the constructor.
Creating a new object is called instantiation.
my_car = Car()
print(my_car)
# <__main__.Car object at 0x10cb08b38>
The object my_car is an instance of the Car class.
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Attributes - Assignment
You can assign values to an instance using dot notation.
my_car = Car()
my_car.make = 'chevy'
my_car.model = 'camaro'
my_car.transmission = 'manual'
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Attributes - Reading
You can also read the value of an attribute using dot notation.
my_car = Car()
print(my_car.make)
# chevy
print(my_car.model)
# 'camaro'
print(my_car.transmission)
# 'manual'
print(my_car.x)
# Traceback (most recent call last):
# File "<stdin>", line 1, in <module>
# AttributeError: 'Car' object has no attribute 'x'
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Passing Object Instances As Arguments
def print_car_details(car):
print("Car make: %s" % car.make)
print("Car model: %s" % car.model)
print("Transmission: %s" % car.transmission)
print_car_details(my_car)
# Car make: chevy
# Car model: camaro
# Transmission: manual
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Classes & Objects
Part 2
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Methods
A method is a function that “belongs to” an object.
class AnnoyingSinger:
def sing(self):
print("Baby shark, do do, do do do do")
pink_fong = AnnoyingSinger()
pink_fong.sing()
# Baby shark, do do, do do do do
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The init() Method
This method is invoked anytime an object is initialized.
class AnnoyingSinger:
def __init__(self, song):
self.song = song
def sing(self):
print(song)
pink_fong = AnnoyingSinger("Baby shark, do do, do do do do")
pink_fong.sing()
# Baby shark, do do, do do do do
frozen = AnnoyingSinger("Let it go, let it go")
frozen.sing()
# Let it go, let it go
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The str() Method
A special method that returns the string representation of a method.
class Person:
def __init__(self, name, age, gender):
self.name = name
self.age = age
self.gender = gender
def __str__(self):
return f"{self.name} identifies as {self.gender} and is {self.age} years old."
john = Person("John", 25, male)
print(john)
# John identifies as male and is 25 years old.
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Classes & Objects
Part 3
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Embedded Objects
An object that is an attribute of another object is embedded.
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Embedded Object Example
class Heart:
def beat(self):
print("ba-dum ba-dum ba-dum")
class Person:
def __init__(self):
self.heart = Heart()
john = Person()
john.heart.beat()
# ba-dum ba-dum
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Classes
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The End
