Can I manually redefine addition and multiplication for Python lists?

Question

I'm working with vectors for small experiments and prototypes in Python. I would like to redefine binary operators like + * - / for Python lists and numbers to mean vector addition, inner product and so on.

I know this is possible with numpy.array or a custom object, but for a small experimental program this makes my code and output cluttered and hard to read.

For example, I want to be able to write:

u=[1,3]
v=[2,-1]
w=2*u+3*v

and have w be the list [8,3]. Is this possible in Python?

Answer 1

You could define a function, such as the following:

def my_add(u, v):
    u = [2*i for i in u]
    v = [3*i for i in v]
    add = [u[i] = v[i] for i in range(2)]
    return add

u = [1, 3]
v = [2, -1]
print(my_add(u, v)) # returns [8,3]

If you want to define your own data type and define its own operators, you can use something called operator overloading. The following is an example:

class Vector:
    def __init__(self, array):
        self.array = array

    def __add__(self, o):
        self.array = [2*i for i in self.array]
        o.array = [3*i for i in o.array]
        return [self.array[i] + o.array[i] for i in range(2)]

u = Vector([1, 3])
v = Vector([2, -1])
print(u+v) # returns [8,3]