python base === member access __len__() and __getitem__()

class A:

    def __init__(self,*args):
        self.name = arg
         pass

    def __len__(self):
        return len(self.name)


a = A("32","asda",435)
print(len(a)) 
# 3    

Returns the "length" of the object instance

 

 

If this __getitem__ method is defined in the class, then its instance object (assumed to be p) can take the value of p[key] like this. When the instance object performs the p[key] operation, the method in the class will be called _ _getitem__.

Generally, if you want to use the index to access elements, you can define this method in the class (__getitem__(self, key) ).

class DataBase:
     ''' class in Python 3 '''

    def  __init__ (self, id, address):
         ''' initialization method ''' 
        self.id = id
        self.address = address
        self.d = {self.id: 1,
                  self.address: "192.168.1.1",
                  }

    def __getitem__(self, key):
        # return self.__dict__.get(key, "100")
        return self.d.get(key, "default")
       

data = DataBase(1, "192.168.2.11")
print(data["hi"])
print(data[data.id])

 

 

 

 

 

References:

https://blog.csdn.net/u013061183/article/details/74773196

https://zhuanlan.zhihu.com/p/27661382