PythonClasses and Objects
Python Classes/Objects
Python is an object oriented programming language.
Almost everything in Python is an object, with its properties and methods.
A Class is like an object constructor, or a "blueprint" for creating objects.
Create a Class
To create a class, use the keywordclass:
Create Object
Now we can use the class named MyClass to create objects:
Example
Create an object named p1, and print the value of x:
print(p1.x)
The __init__() Function
The examples above are classes and objects in their simplest form, and are not really useful in real life applications.
To understand the meaning of classes we have to understand the built-in__init__() function.
All classes have a function called__init__(), which is always executed when the class is being initiated.
Use the__init__() function to assign values to object properties, or other operations that are necessary to do when the object is being created:
Example
Create a class named Person, use the__init__() function to assign values for name and age:
def __init__(self, name, age):
self.name = name
self.age = age
p1 = Person("John", 36)
print(p1.name)
print(p1.age)
Note: The__init__() function is called automatically every time the class is being used to create a new object.
The __str__() Function
The__str__() function controls what should be returned when the class object is represented as a string.
If the__str__() function is not set, the string representation of the object is returned:
Example
The string representation of an object WITHOUT the__str__() function:
def __init__(self, name, age):
self.name = name
self.age = age
p1 = Person("John", 36)
print(p1)
Example
The string representation of an object WITH the__str__() function:
def __init__(self, name, age):
self.name = name
self.age = age
def __str__(self):
return f"{self.name}({self.age})"
p1 = Person("John", 36)
print(p1)
Object Methods
Objects can also contain methods. Methods in objects are functions that belong to the object.
Let us create a method in the Person class:
Example
Insert a function that prints a greeting, and execute it on the p1 object:
def __init__(self, name, age):
self.name = name
self.age = age
def myfunc(self):
print("Hello my name is " + self.name)
p1 = Person("John", 36)
p1.myfunc()
Note: Theself parameter is a reference to the current instance of the class, and is used to access variables that belong to the class.
The self Parameter
Theself parameter is a reference to the current instance of the class, and is used to access variables that belong to the class.
It does not have to be namedself, you can call it whatever you like, but it has to be the first parameter of any function in the class:
Example
Use the wordsmysillyobject andabc instead ofself:
def __init__(mysillyobject, name, age):
mysillyobject.name = name
mysillyobject.age = age
def myfunc(abc):
print("Hello my name is " + abc.name)
p1 = Person("John", 36)
p1.myfunc()
Modify Object Properties
You can modify properties on objects like this:
Delete Object Properties
You can delete properties on objects by using thedel keyword:
Delete Objects
You can delete objects by using thedel keyword:
The pass Statement
class definitions cannot be empty, but if you for some reason have aclass definition with no content, put in thepass statement to avoid getting an error.
