Python Class Methods
Methods are functions that belong to a class. They define the behavior of objects created from the class.
Example
Create a method in a class:
class Person:
def __init__(self, name):
self.name = name
def greet(self):
print("Hello, my name is " + self.name)
p1 = Person("Emil")
p1.greet()Note: All methods must have self as the first parameter.
Methods with Parameters
Methods can accept parameters just like regular functions:
Example
Create a method with parameters:
class Calculator:
def add(self, a, b):
return a + b
def multiply(self, a, b):
return a * b
calc = Calculator()
print(calc.add(5, 3))
print(calc.multiply(4, 7))Methods Accessing Properties
Methods can access and modify object properties using self:
Example
A method that accesses object properties:
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def get_info(self):
return f"{self.name} is {self.age} years old"
p1 = Person("Tobias", 28)
print(p1.get_info())Methods Modifying Properties
Methods can modify the properties of an object:
Example
A method that changes a property value:
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def celebrate_birthday(self):
self.age += 1
print(f"Happy birthday! You are now {self.age}")
p1 = Person("Linus", 25)
p1.celebrate_birthday()
p1.celebrate_birthday()The __str__() Method
The __str__() method is a special method that controls what is returned when the object is printed:
Example
Without the __str__() method:
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
p1 = Person("Emil", 36)
print(p1)Example
With the __str__() method:
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def __str__(self):
return f"{self.name} ({self.age})"
p1 = Person("Tobias", 36)
print(p1)Multiple Methods
A class can have multiple methods that work together:
class Playlist:
def __init__(self, name):
self.name = name
self.songs = []
def add_song(self, song):
self.songs.append(song)
print(f"Added: {song}")
def remove_song(self, song):
if song in self.songs:
self.songs.remove(song)
print(f"Removed: {song}")
def show_songs(self):
print(f"Playlist '{self.name}':")
for song in self.songs:
print(f"- {song}")
my_playlist = Playlist("Favorites")
my_playlist.add_song("Bohemian Rhapsody")
my_playlist.add_song("Stairway to Heaven")
my_playlist.show_songs()Delete Methods
You can delete methods from a class using the del keyword:
class Person:
def __init__(self, name):
self.name = name
def greet(self):
print("Hello!")
p1 = Person("Emil")
del Person.greet
p1.greet() # This will cause an errorPython Inner Classes
An inner class is a class defined inside another class. The inner class can access the properties and methods of the outer class.
Inner classes are useful for grouping classes that are only used in one place, making your code more organized.
Example
Create an inner class:
class Outer:
def __init__(self):
self.name = "Outer Class"
class Inner:
def __init__(self):
self.name = "Inner Class"
def display(self):
print("This is the inner class")
outer = Outer()
print(outer.name)Accessing Inner Class from the Outside
To access the inner class, create an object of the outer class, and then create an object of the inner class:
class Outer:
def __init__(self):
self.name = "Outer"
class Inner:
def __init__(self):
self.name = "Inner"
def display(self):
print("Hello from inner class")
outer = Outer()
inner = outer.Inner()
inner.display()Accessing Outer Class from Inner Class
Inner classes in Python do not automatically have access to the outer class instance. If you want the inner class to access the outer class, you need to pass the outer class instance as a parameter:
class Outer:
def __init__(self):
self.name = "Emil"
class Inner:
def __init__(self, outer):
self.outer = outer
def display(self):
print(f"Outer class name: {self.outer.name}")
outer = Outer()
inner = outer.Inner(outer)
inner.display()Practical Example
Inner classes are useful for creating helper classes that are only used within the context of the outer class:
class Car:
def __init__(self, brand, model):
self.brand = brand
self.model = model
self.engine = self.Engine()
class Engine:
def __init__(self):
self.status = "Off"
def start(self):
self.status = "Running"
print("Engine started")
def stop(self):
self.status = "Off"
print("Engine stopped")
def drive(self):
if self.engine.status == "Running":
print(f"Driving the {self.brand} {self.model}")
else:
print("Start the engine first!")
car = Car("Toyota", "Corolla")
car.drive()
car.engine.start()
car.drive()