Python Classes 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 keyword class:
Example
Create a class named MyClass, with a property named x:
class MyClass:
x = 5
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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:
p1 = MyClass()
print(p1.x)
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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:
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
p1 = Person("John",
36)
print(p1.name)
print(p1.age)
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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:
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
p1 = Person("John",
36)
print(p1)
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Example
The string representation of an object WITH the __str__() function:
class Person:
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)
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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:
class Person:
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()
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Note: The self 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
The self 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 named self, you can
call it whatever you like, but it has to be the first parameter of any function
in the class:
Example
Use the words mysillyobject and abc instead of self:
class Person:
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()
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Modify Object Properties
You can modify properties on objects like this:
Delete Object Properties
You can delete properties on objects by using the
del keyword:
Delete Objects
You can delete objects by using the del keyword:
The pass Statement
class definitions cannot be empty, but if
you for some reason have a class definition with no content, put in the pass statement to avoid getting an error.
