Array and __rmul__ operator in Python Numpy

Question

In a project, I created a class, and I needed an operation between this new class and a real matrix, so I overloaded the __rmul__ function like this

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Answer 1

You can define __numpy_ufunc__ function in your class. It works even without subclassing the np.ndarray. You can find the documentation here.

Here is an example based on your case:

class foo(object):

    aarg = 0

    def __init__(self):
        self.aarg = 1

    def __numpy_ufunc__(self, *args):
        pass

    def __rmul__(self,A):
        print(A)
        return 0

    def __mul__(self,A):
        print(A)
        return 0

And if we try it,

A = [[i*j for i in np.arange(2)  ] for j in np.arange(3)]
A = np.array(A)
R = foo()
C =  A * R

Output:

[[0 0]
 [0 1]
 [0 2]]

It works!