How to use class in python

The concept of class in Python programming can be compared to the description of a certain type of collection. For example, "human beings" can be regarded as a class, and then the human class is used to define each specific person-you, me, him. etc. as its object. Classes also have attributes and functions. Attributes are some characteristics of the class itself. For example, humans have attributes such as name, height, and weight, and the specific values ​​​​will vary according to each person; functions are the behaviors that the class can achieve, such as humans have Functions such as eating, walking and sleeping.

The specific form is as follows:

# Example: The concept of class
class Human being:
Name = ' Unnamed' # Member variable
def speak (content): # Member function
                                                                                                                                                                                                                                             Member variable # Someone. Name = "Passenger A"
Someone. Speak ('Hello everyone') # Passer-by A speaks
>>> Hello everyone! #Output


Sample program one (class definition):

>>> class pp:
...     pass
...
>>> p = pp()
>>> print p
<__main__.pp instance at 0x00CA77B0>
>>>

prints the type of this variable. It tells us that we already have an instance of the Person class in the __main__ module.

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Sample program two (__init__ usage):

Description: __init_ The _ method is run immediately when the object of the class is created. This method is used to initialize the object.

>>> class Person:
...     def __init__(self, name):
...             self.name = name
...     def sayHi(self):
...             print 'Hello, my name is', self.name
...
>>> p = Person('Swaroop')
>>> p.sayHi()
Hello, my name is Swaroop
>>>

Sample program three (__del__ method):

Explanation: The __del__ method is called when the program exits.

>>> class Person:
...     population = 0
...     def __init__(self, name):
...             self.name = name
...             print '(Initializing %s)' % self.name
...     def __del__(self):
...             print '%s says bye.' % self.name
...             Person.population -= 1
...
...     def howMany(self):
...             if Person.population == 1:
...                     print 'I am the only person here.'
...             else:
...                     print 'We have %d persons here.' % Person.population
...
>>> A = Person('aa')
(Initializing aa)
>>> A.howMany()
We have 0 persons here.
>>> B = Person('bb')
(Initializing bb)
>>> B.howMany()
We have 0 persons here.
>>> ^Z
aa says bye.
bb says bye.

The form of defining and using classes in Python is: class class name [(parent class name)]:[member function and member variable], the class name is the name of this class, and the parent class The name is optional, but after defining the parent class name, the subclass will have the corresponding attributes and methods of the parent class. When a class is defined as an object, the __init__ constructor will be called first to initialize the attributes of the object. Each attribute (member variable) of the class can be defined in the constructor. Just add the object pointer when defining it. . When the object is destroyed, the __del__ destructor will be called. When defining a member function of a class, a variable (similar to the this pointer in C) must be defaulted to represent the object defined by the class itself. The name of this variable can be defined by yourself. , the following example will use the self variable to represent the class object variable.

# Example: Class Definition and Usage

class CAnimal: 
   name = 'unname' # 成员变量 
def __init__(self,voice='hello'): # 重载构造函数 
   self.voice = voice # 创建成员变量并赋初始值 
def __del__(self): # 重载析构函数 
       pass # 空操作 
def Say(self): 
   print self.voice 
t = CAnimal() # 定义动物对象t 
t.Say() # t说话 
>> hello # 输出 
dog = CAnimal('wow') # 定义动物对象dog 
dog.Say() # dog说话 
>> wow # 输出

In Python programming, classes can inherit parent class attributes in the form of class class name (parent class ), the subclass can inherit all methods and attributes of the parent class, and can also overload the member functions and attributes of the parent class. It should be noted that if the member function of the subclass overrides the parent class (that is, the name is the same), the subclass will be used Member function

# Example: Class inheritance

class CAnimal: 
        def __init__(self,voice='hello'): # voice初始化默认为hello 
              self.voice = voice 
        def Say(self): 
            print self.voice 
  def Run(self): 
            pass # 空操作语句（不做任何操作） 
class CDog(CAnimal): # 继承类CAnimal 
    def SetVoice(self,voice): # 子类增加函数
          SetVoice self.voice = voice 
       def Run(self,voice): # 子类重载函数Run

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