開始寫部落格吧！Start writing!

參考網站：
https://www.w3schools.com/python/python_classes.asp

什麼是Class & Object?

官方介紹

“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.

---

創建類別 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

print(MyClass)

輸出結果

	
<class '__main__.MyClass'>

---

創建對象 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:

class MyClass:
  x = 5

p1 = MyClass()
print(p1.x)

輸出結果

	
5

---

__init__() 函數:

Note: The __init__() function is called automatically every time the class is being used to create a new object.

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)

	
John
36

---

__str__() 函數:

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)

	
# <__main__.Person object at 0x15039e602100>

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)

	
# John(36)

---

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()

	
# Hello my name is John

---

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()

輸出結果

Hello my name is John

---

Modify Object Properties :

You can modify properties on objects like this:

Example

Set the age of p1 to 40:

p1.age = 40

---

Delete Object Properties :

You can delete properties on objects by using the del keyword:

Example

Delete the age property from the p1 object:

del p1.age

---

Delete Objects :

You can delete objects by using the del keyword:

Example

Delete the p1 object:

del p1

---

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.

Example

class Person:
  pass

---

转载请注明来源，欢迎对文章中的引用来源进行考证，欢迎指出任何有错误或不够清晰的表达。可以邮件至 kimfei2014@gmail.com