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On section describes __new __ () method that is more important than the constructor method syntax, this section analyzes in detail through case __new __ (relationship between the details of the method and its structure and methods).
First, the case described
in this section Cir Case of a circle described, to illustrate the problem of class defines only the basic information contains only one member of the radius RADIUS, two methods, that is __new __ () methods and constructors __init __ () method .
For easy viewing information, we will return the relevant parameters and information output value.
Second, the case of the code
1. class definition
class Cir():
def __new__(cls,*args,**kwargs):
#看看Python传递给__new__的参数
print("Python传递给__new__的参数:\n***cls: ",cls,"\n***args: ",args,"\n***kwargs:",kwargs)
inst = super().__new__(cls)
print("__new__返回值:",inst)
return inst
def __init__(self,radius):
print("In init,self的值为:",self,", radius的值为：",radius)
self.radius = radius
2. Create an instance of the class and View (interactive mode execution)
c=Cir(10)
c #查看c的数据
Cir #查看类的数据3. Case screenshots and interpretation
As can be seen from the above screenshot following three points:
. 1) before the method is performed __new__ __init__ method;
2) from where it can be seen in the above figure labeled red pen, __ call the parent class method returns new__ in __new__ examples of self inst value and the init, c and instances created after the value at the address is the same, show a three, and is returned by the method of the parent class __new__;
3) from the above figure yellow mark portion, can be seen the method of the parameters is cls __new__ Cir corresponding class.
This section describes the case by __new __ () method and the relationship between the portion __init__ method, summarized as follows:
1. __new__ is performed before the method __init__ method, after __ new__ method returns an instance of an object execution, i.e. ; said __new__ method before executing instance did not create, parameter self constructor is passed after the last instance of execution __new__ method
parameter 2. __new__ method is automatically passed by the Python, the parameters include creating instances the "class name" corresponding to the class, and create instances create all the parameters passed.
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