Overrides for built-in methods in Python classes

Some of the built-in methods are often rewritten in the class for the purpose, most commonly such as __setattr__, with built-in properties to see what happens to overrides

First define a test class with the following code

class Base:     def __init__ (self):         Pass  #  View built-in properties

Printing results are as follows

('__class__', <class 'type'>)('__delattr__', <slot Wrapper'__delattr__'Of'Object'Objects>)('__dict__', Mappingproxy ({'__module__':'__main__','__init__': <function base.__init__At 0x0069a0c0>'__getattr__': <function base.__getattr__At 0x0069a108>'__dict__': <attribute'__dict__'Of'Base'Objects>,'__weakref__': <attribute'__weakref__'Of'Base'Objects>,'__doc__': None})) ('__dir__', <method'__dir__'Of'Object'Objects>)('__doc__', None) ('__eq__', <slot Wrapper'__eq__'Of'Object'Objects>)('__format__', <method'__format__'Of'Object'Objects>)('__ge__', <slot Wrapper'__ge__'Of'Object'Objects>)('__getattr__', <function base.__getattr__At 0x0069a108>)('__getattribute__', <slot Wrapper'__getattribute__'Of'Object'Objects>)('__gt__', <slot Wrapper'__gt__'Of'Object'Objects>)('__hash__', <slot Wrapper'__hash__'Of'Object'Objects>)('__init__', <function base.__init__At 0x0069a0c0>)('__init_subclass__', <built-inchMethod__init_subclass__of type Object at 0x00699030>)('__le__', <slot Wrapper'__le__'Of'Object'Objects>)('__lt__', <slot Wrapper'__lt__'Of'Object'Objects>)('__module__','__main__')('__ne__', <slot Wrapper'__ne__'Of'Object'Objects>)('__new__', <built-inchMethod__new__of type Object at 0x1e1fadb8>)('__reduce__', <method'__reduce__'Of'Object'Objects>)('__reduce_ex__', <method'__reduce_ex__'Of'Object'Objects>)('__repr__', <slot Wrapper'__repr__'Of'Object'Objects>)('__setattr__', <slot Wrapper'__setattr__'Of'Object'Objects>)('__sizeof__', <method'__sizeof__'Of'Object'Objects>)('__str__', <slot Wrapper'__str__'Of'Object'Objects>)('__subclasshook__', <built-inchMethod__subclasshook__of type Object at 0x00699030>)('__weakref__', <attribute'__weakref__'Of'Base'objects>)

built-in properties for base

Find __setattr__ and find that he is a slot wrapper (can be understood as a socket wrapper)

' __setattr__ ' ' __setattr__ ' ' Object ' objects>

Rewrite the __setattr__ to print key and value at the time of assignment

def __setattr__ (self, Key, value):     Print (Key,value) self    . __dict__ [Key] = value

Print again and find __setattr__ a common method

('__setattr__', <function base. __setattr__ at 0x0227f108>)

Summary : When overriding a built-in method, the built-in method changes from slot wrapper to normal function,slot wrapper-->function

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question : If there is a class inheritance, the parent class overrides, does the subclass also inherit?

1 classBase#Parent Class2     def __init__(self):3         Pass4 5     def __setattr__(self, Key, value):6         Print(key, value)7Self.__dict__[Key] =value8 9 classFoo (Base):#sub-classTen     def __init__(self): One         Pass

Subclass Foo Not overridden method

Scenario 1: Subclass Foo does not rewrite __setattr__, the parent class is __setattr__ exactly the same as the built-in properties of the subclass Foo

# Parent class Base ('__setattr__', <function base. __setattr__ at 0x0243e108>)#  sub-class foo('__setattr__') , <function base. __setattr__ at 0x0243e108>)

Case 2, subclass Foo overrides the __setattr__ method, which is different

# Parent class Base ('__setattr__', <function base. __setattr__ at 0x0243e108>)#  sub-class foo('__setattr__') , <function Foo. __setattr__ at 0x022be198>)

, summary : When there is an inheritance relationship, 1: The parent class overriding the built-in method affects all subclasses

2: Subclasses overwrite methods with inheritance attributes, overwriting the same method of the parent class

3: In multiple inheritance, if the parent class overrides the method, it inherits the method written in the previous parent class (refer to my other article on multiple inheritance)

Overrides for built-in methods in Python classes