Preface
Before we have learned the basic data types, functions and file reading and writing of Python, then we will take a look at Python's object-oriented programming. If you have learned an object-oriented programming language similar to Java, compare it with Python Object-oriented will feel very easy. As a scripting language, Python is more concise and convenient than Java in object-oriented, and has a lot of constraints.
Create object
Like other languages, Python uses the class keyword to declare a class. The name of the class uses camel case with the first letter capitalized.
class Animal:
def __init__(self, name, age):
self.name = name
self.age = age
def run(self):
print(self.name + " is running")
__init__()Method is essential, this is to instantiate the object
As shown in the code above, the
__init__()methods in the Pyhton class are indispensable, which are initialized to instantiate objects, a bit similar to the constructor in Java.__init__()Self is indispensable in the method, and must be placed first, it is a reference to itself.
Create instance
Python uses the following methods to instantiate objects without using the new keyword.
class Animal:
def __init__(self, name, age):
self.name = name
self.age = age
def run(self):
print(self.name + " is running")
dog = Animal('lily', 2)
Access properties and methods
Attributes and methods in Python can be directly accessed
class Animal:
def __init__(self, name, age):
self.name = name
self.age = age
def run(self):
print(self.name + " is running")
dog = Animal('lily', 2)
print(dog.age)
print(dog.name)
dog.run()
Add default values to attributes
Python can set default values for attributes, so you don't need to pass in parameters during initialization.
class Animal:
def __init__(self, age):
self.name = 'Lily'
self.age = age
def run(self):
print(self.name + " is running")
Modify the value of the attribute
Pyhton can modify the value of an attribute in two ways. First, you can modify the attribute value through direct access.
class Animal:
def __init__(self, name, age):
self.name = name
self.age = age
def run(self):
print(self.name + " is running")
dog = Animal('lily', 2)
dog.name = 'Harry'
dog.age = 3
print(dog.age)
print(dog.name)
dog.run()
The result is shown below
You can also change the property value through methods, similar to the setter in Java.
class Animal:
def __init__(self, name, age):
self.name = name
self.age = age
def run(self):
print(self.name + " is running")
def update_name(self, name):
self.name = name
Dog = Animal('Harry', 2)
Dog.update_name('Lily')
Dog.run()
Inherit the parent class
Inheritance is also possible in Python, but instead of using the extends keyword, parentheses are used directly. Which
super().__init__(name, age)links the child class with the parent class.
class Animal:
def __init__(self, name, age):
self.name = name
self.age = age
def run(self):
print(self.name + " is running")
class Dog(Animal):
def __init__(self, name, age, leg):
super().__init__(name, age)
self.leg = 4
Harry = Dog("Harry", 2, 4)
print(Harry.leg)
Rewrite method
The rewriting method in Python is relatively simple. If the subclass has a function with the same name as the parent class, the instance of the subclass directly calls the function of the subclass when the function is called.
class Animal:
def __init__(self, name, age):
self.name = name
self.age = age
def run(self):
print(self.name + " is running")
def update_name(self, name):
self.name = name
class Dog(Animal):
def __init__(self, name, age, leg):
super().__init__(name, age)
self.leg = 4
def run(self):
print("Dog is running")
Harry = Dog("Harry", 2, 4)
Harry.run()
At last
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