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python class inheritance explanation

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Release： 2017-04-02 13:18:00

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For many articles explaining inheritance of python classes, most of them talk about concepts such as oop and polymorphism. I think this may be helpful to developers with a certain foundation. It's not that big. It's better to directly use the code written in various situations to show the effect of running the code for a certain code situation. This may be more helpful to developers. Don’t talk nonsense, just go straight to the code.

There is no distinction between classic classes and new-style classes. The following analysis applies to both new-style classes and classic classes.

For the init

function in the class, it is just an initialization call a function (ps: initialization and instance creation are not a process, the creation of the instance is completed through a create function), if there is no explicit declaration of the init function in the subclass, the subclass will call the init of the parent class function, but the init function in the parent class of the parent class will not be called again. If the init function is explicitly declared, the initialization function of the parent class will not be called during the initialization of the subclass, only the declaration in the subclass will be called. init function, and at the same time, in the subclass instance, there will be no attribute declared in the parent class init function. Example:

class animal():
    name="hh"
    sex="man"
    def init(self):        self.height=10
        self.weight=50
    def deception(self):
        print "ansible.height:"+self.height+" animal.weight:"+self.weight    def run(self):
        print "animal is running...."class dog(animal):
    def init(self):
        passif name=="main":
   dg=dog()
   print dg.dict

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The result of running at this time is

{}

When the dog class is modified as follows (ps: there is no explicit declaration of the init method at this time):

class dog(animal):
    def run(self):
        print "dog is running..."

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At this time, due to the direct call of the init of the parent class animal method, the results are as follows:

{'weight': 50, 'height': 10}

What will happen if a class inherits the dog class at this time? ? (The Python interpreter first searches for the init method in the subclass. If it is not found, it then searches for it in the parent class until it is found and runs it. It will no longer run the init method of the parent class of the parent class. There is no init running at this time. There are no attributes created in the method. For example, in the above example, the example obtained when running for the first time does not have the weight and height attributes)

class animal():
    name="hh"
    sex=""
    def init(self):        self.height=10
        self.weight=50
    def deception(self):
        print "ansible.height:"+self.height+" animal.weight:"+self.weight    def run(self):
        print "animal is running...."class dog(animal):
    def init(self):
        pass    def run(self):
        print "dog is running..."class jinmao(dog):
    # def init(self):
    #     self.ji="jinmao"
    passif name=="main":
   dg=jinmao()
   print dg.dict

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The result at this time is the same

{}

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What happens in multiple inheritance of classes? (In multiple inheritance, the init function in the parent class declared by the first parameter in the inheritance parameter of the class will be run. If there is no init function in the parent class, continue to look for the init function in the parent class of the parent class, and so on. . If the header is found or not, it is replaced by the parent class declared by the second parameter. The process is the same as the first parameter until the init function is found. If no header is found, it is not initialized.) The code can be tested by yourself based on the previous example. .

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