Detailed example of class inheritance in Python

This article mainly introduces relevant information about the detailed explanation of inheritance examples of python classes. Friends who need it can refer to

Inheritance of python classes

For many articles When explaining the inheritance of python classes, most of them talk about concepts such as oop and polymorphism. I think this may not be that helpful to developers with a certain foundation. It is better to directly use the code written in various situations. Shows 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 It is a function called (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__ function of the parent class, 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 of the parent class will not be called during the initialization of the subclass. function will only call the __init__ function declared in the subclass. At the same time, there will be no attributes declared in the __init__ function of the parent class in the subclass instance.

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):
  pass
if __name__=="__main__":
 dg=dog()
 print dg.__dict__

The result of running at this time is

{}

When the dog class is modified as follows (ps: there is no displayed declaration __init__ method at this time):

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

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

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

If a class inherits the dog class at this time, what will happen 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. At this time There are no attributes created in the __init__ method that has not been run. For example, in the above example, the weight and height attributes are not included in the example obtained when running for the first time)

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"
 pass
if __name__=="__main__":
 dg=jinmao()
 print dg.__dict__

The result at this time is the same

{}

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 search to see if there is one in the parent class of the parent class. And so on. . . . If the header is found but not found, then the parent class declared by the second parameter is used. The process is as follows until the __init__ function is found. If neither is found, the code is not initialized. You can test it yourself based on the previous example.

The use and characteristics of super for calling methods in the parent class in the subclass.

Summary: If you want to know how the python virtual machine creates classes (specifically, when loading a .pyc file, how to use the code logic of c language to Class objects are placed in a piece of memory. I am also learning about this aspect and hope we can explore together)

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