Python class inheritance and subclass instance initialization usage analysis

The examples in this article describe the Python class inheritance and subclass instance initialization usage. Share to everyone for your reference. The specific analysis is as follows:

[First reference book original (Chinese-English control)]
__init__ Method Description:
If a base class has a __init__ () method The derived class ' s __init__ () method must explicitly call it to ensure proper in Itialization of the base class part of the instance; For example: "Baseclass.__init__ (self, [args ...])"
As a special contraint on constructors, no value is returned; Doing so would cause a TypeError to being raised at runtime.

If its base class also has __init__ (), it must be explicitly called in __init__ () to ensure that its base class part is properly initialized, for example: "Baseclass.__init__ (self, [args ...])" As a special case of a constructor, it has no value returned, and if a value is returned, an exception TypeError is thrown at run time.

1. When the subclass defines the __init__ method, if the call base class __init__ method is not displayed, Python does not call for you, explaining that the run is OK

Class A ():  def __init__ (self):    print ' A ' class B (a):  def __init__ (self):    print ' B ' if __name__== ' __main __ ':  b=b () >>> b

2. When the subclass does not define the __init__ method, Python will automatically help you invoke the __init__ method of the first base class, with the first note. That is, when a subclass inherits from more than one base class, only the __init__ method of the first base class is called to:

Class A:  def __init__ (self):    print ' A ' class B:  def __init__ (self):    print ' B ' class C (b):  def __init __ (self):    print ' C '  passclass D1 (a,b,c):  passclass D2 (b,a,c):  passclass D3 (c,b,a):  passif (__ name__== ' __main__ '):  print ' D1-------;: '  d1=d1 ()  print ' D2-------;: '  d2=d2 ()  print ' d3-------: '  d3=d3 () >>> d1------->:ad2------->:bd3------->:c

3) When the __init__ method is not defined by the base class, when the subclass shows the call to the base class __init__ method, Python goes up and calls the __init__ method of the base class of the base class, essentially the same as 2

Class A:  def __init__ (self):    print ' A ' class B:  def __init__ (self):    print ' B ' class C1 (b,a):  Passclass C2 (A, B):  passclass D1 (C1):  def __init__ (self):    c1.__init__ (Self) class D2 (C2):  def __init_ _ (Self):    c2.__init__ (self) if (__name__== ' __main__ '):  print ' D1-------;: '  d1=d1 ()  print ' D2-------: '  d2=d2 () >>> d1------->:bd2------->:a

Hopefully this article will help you with Python programming.

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