Python class inheritance and initialization usage analysis of subclass instances _python

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

[The original reference books (Chinese and English)]
__init__ Method Introduction:
If a base class has an __init__ () method The derived class "s __init__ () method must explicitly call it to ensure prope R initialization of the base class part of the instance; For example: "Baseclass.__init__ (self, [args ...])"
As a special contraint on constructors, no value may be returned; Doing so'll cause a typeerror to is raised at runtime.

If its base class also has __init__ (), it must be explicitly invoked at __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. Subclasses define the __init__ method, if the call to the base class __init__ method is not displayed, Python will not help you invoke, explain run all OK

Class A ():
  def __init__ (self):
    print ' A '
class B (a):
  def __init__ (self):
    print ' B '
if __name_ _== ' __main__ ':
  b=b ()
>>> 
b

2. When subclasses do not define the __init__ method, Python automatically invokes the first base class __init__ method. That is, when a subclass inherits from multiple base classes, only the __init__ method of the first base class is invoked to:

Class A:
  def __init__ (self):
    print ' A '
class B:
  def __init__ (self):
    print ' B '
class C (b):
  def __init__ (self):
    print ' C '
  pass
class D1 (a,b,c):
  Pass
class D2 (b,a,c):
  Pass
class D3 (c,b,a):
  pass
if (__name__== ' __main__ '):
  print ' d1-------: '
  d1=d1 ()
  print ' d2-------: '
  d2=d2 ()
  print ' d3-------: '
  d3=d3 ()
>>> 
d1------- :
a
d2-------:
B
D3-------:
C

3 when the __init__ method is not defined by the base class, if the subclass shows the invocation of the base class __init__ method, Python goes up to the __init__ method of the base class of the basis classes and invokes it in real terms with 2

Class A:
  def __init__ (self):
    print ' A '
class B:
  def __init__ (self):
    print ' B '
class C1 (b,a):
  Pass
class C2 (a,b):
  Pass
class 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-------:
b
D2-------:
A

I hope this article will help you with your Python programming.