curriculum/challenges/english/blocks/lecture-classes-and-objects/68420bd261d0d35f61922d4b.md
In Python, classes and objects work hand in hand to organize and manage data. You build a class to define shared behavior, then create objects that use those behaviors.
In other words, a class is like a blueprint or template you use to create objects with.
Let's look at what classes are, and how to use them to create objects.
To create a class, you use the class keyword followed by the name of the class and a colon. Then within the class, you can add an initializer, along with any attributes and methods.
Attributes are like variables within a class, and are used to store data. Methods are functions defined within a class, and are the actions objects created with a class can perform.
Here's the basic syntax of a class:
class ClassName:
def __init__(self, name, age):
self.name = name
self.age = age
def sample_method(self):
print(self.name.upper())
class ClassName is made up of the class keyword to create a class, followed by the name of the class, here called ClassName. It is common in Python to use the PascalCase convention when naming classes.
def __init__(self, name, age) is the special method automatically called when a new object is created. It initializes the attributes of the objects that will be created with the class.
In addition to that, the first parameter of __init__ is always a reference to the specific object being created or used. By convention, this parameter is named self, but technically, you can use any name. self lets you access the object's own attributes and methods.
self.name = name and self.age = age are the attributes the objects will have.
def sample_method(self): is the method each object created can call.
print(self.name.upper()) is what the sample_method method will do, in this case, it prints the name in uppercase.
If that all sounds like a lot, don't worry. Let's take a look at a similar example of a Dog class, and how you can create objects from that:
class Dog:
def __init__(self, name, age):
self.name = name
self.age = age
def bark(self):
print(f"{self.name.upper()} says woof woof!")
With this Dog class, you can create an object. Here's the basic syntax for creating objects from a class:
object_1 = ClassName(attribute_1, attribute_2)
object_2 = ClassName(attribute_1, attribute_2)
You can also call any of the methods defined in the class from each object:
object_1.method_name()
object_2.method_name()
Now let's create two dogs by using the Dog class as the blueprint:
class Dog:
def __init__(self, name, age):
self.name = name
self.age = age
def bark(self):
print(f"{self.name.upper()} says woof woof! I'm {self.age} years old!")
dog_1 = Dog("Jack", 3)
dog_2 = Dog("Thatcher", 5)
# Call the bark method
dog_1.bark() # JACK says woof woof! I'm 3 years old!
dog_2.bark() # THATCHER says woof woof! I'm 5 years old!
As you can see, we create two dog objects using the Dog class. When initializing dog_1, the string Jack and the number 3 are passed, which sets the name and age attributes for that instance. And dog_2 is initialized with the string Thatcher and number 5 as its name and age, respectively.
Then when you call the .bark() method on dog_1 and dog_2, you can see how both outputs differ, and use the unique name and age attributes you passed in when creating each object.
In summary, the difference between a class and an object is that a class is the template or the blueprint, and an object is what is created using that template.
Also, a class defines what data and behavior the object should have, and an object holds the actual data and uses that behavior. You write a class once, and you can make many objects from it, each with different data.
What is the output of this code?
class Dog:
def __init__(self, name):
self.name = name
def bark(self):
print(f"{self.name} says Woof!")
my_dog = Dog("Rex")
print(my_dog.name)
Rex says Woof!
Look at what is being printed: is it calling a method or accessing an attribute?
name
Look at what is being printed: is it calling a method or accessing an attribute?
Rex
Error
Look at what is being printed: is it calling a method or accessing an attribute?
3
What is the special method that gets automatically called when a new object is created?
__create_object__
Think about what initializes the attributes an object will have.
__init__
__new__
Think about what initializes the attributes an object will have.
__setup__
Think about what initializes the attributes an object will have.
2
What is the blueprint or template for creating objects?
A variable
Think about what defines the structure and behavior of objects created from it.
A function
Think about what defines the structure and behavior of objects created from it.
A class
A loop
Think about what defines the structure and behavior of objects created from it.
3