I am using Python and I am trying to construct a class, say Numbers, using Subclassing ndarray. I wish my class satisfies two following properties:

• All the methods of numpy is applicable to my class Numbers. (This is the reason why I chose to use Subclassing ndarray.)
• Every times I perform the addition between two instances of class Numbers, I can cumulatively record the number of additions I have used.

Here is what I tried

import numpy as np

class Numbers(np.ndarray):

    nb_add = 0

    def __new__(cls, values):
        self = np.asarray(values).view(cls)
        return self 

    def __add__(self, new_numbers):
        Numbers.nb_add  = len(new_numbers)
        return self   new_numbers

a = Numbers([1,2,3,4])
b = Numbers([5,6,7,8])
c = a b 
print(a.reshape(2, 2)) # expect [[1,2], [3,4]]
print(Numbers.nb_add)# expect 4 = number of addtions

But the method __add__ leads to error.

I found a similar post here, but it is not the case I am looking for.

Could anyone help me? Thanks!

CodePudding user response：

The problem is that the expression self new_numbers is referencing the __add__ method of Numbers and hence the method calls itself. If you explicitly call the __add__ method of the base class, then you get the result you want:

import numpy as np

class Numbers(np.ndarray):

    nb_add = 0

    def __new__(cls, values):
        self = np.asarray(values).view(cls)
        return self

    def __add__(self, new_numbers):
        Numbers.nb_add  = len(new_numbers)
        return np.ndarray.__add__(self,new_numbers)

a = Numbers([1,2,3,4])
b = Numbers([5,6,7,8])
c = a b 
print(a.reshape(2, 2)) # expect [[1,2], [3,4]]
print(Numbers.nb_add)# expect 4 = number of addtions