Methods of using property attributes in old Python classes

In Python, we can intercept all of the object's feature accesses. With this interception idea, we can implement the property method in the old class.

__getattribute__ # called automatically when the attribute name is accessed (can only be used in modern classes) __getattr__ # called automatically when the attribute name is accessed and the object does not have a corresponding attribute __setattr__ # automatically called when attempting to assign a value to an attribute name __delattr__ # automatically called when an attribute name is attempted to be deleted # * Compared to the use of property is a bit complex, but the special method uses very wide

Here is an example:

classDemo5 (object):def __init__(self):Print("This is a constructor") self._value1=None self._value2=Nonedef __setattr__(self, Key, value):Print("try to set the value of the%s property"%(key,))ifKey = ='NewValue': self._value1, Self._value2=valueElse:            Print("The property key isn't NewValue, now create or set it through __dict__") self.__dict__[Key] =valuedef __getattr__(self, item):Print("try to get the value of%s"%(item,))ifitem = ='NewValue':            returnself._value1, Self._value2Else:            Print("The %s Item is not exist"%(item,))#Raise Attributeerror    def __delattr__(self, item):ifitem = ='NewValue':            Print("Delete the value of NewValue")            delself._value1delself._value2Else:            Print("Delete other values, the value of name is%s"%Item)if __name__=="__main__": Testdemo=Demo5 ()Print(testdemo.newvalue) Testdemo.newvalue="name","HelloWorld"    Print("Print the value of the property:", Testdemo.newvalue)Print(testdemo.notexist)delTestdemo.newvalue

Here's the result:

This is a constructorTryTo set the value of the _value1 propertythe property key is  notNewValue, now createorSet it Through__dict__TryTo set the value of the _value2 propertythe property key is  notNewValue, now createorSet it Through__dict__Tryto get the value of NewValue (none, none)TryTo set the value of the NewValue propertyTryTo set the value of the _value1 propertythe property key is  notNewValue, now createorSet it Through__dict__TryTo set the value of the _value2 propertythe property key is  notNewValue, now createorSet it Through__dict__TryTo get the value of NewValue ('Print the value of the property:', ('name','HelloWorld'))TryTo get the value of Notexist the Notexist item is  notExistnonedelete The value of newvaluedelete other values, the value name is_value1delete Other values, the value name is_value2

* * In fact, we can see that when using __setatter__, __getatter__,__delatter__ These interfaces will have an impact on other values because this is a generic interface that must be called.

Methods of using property attributes in old Python classes