Python: How to pass more than one argument to the property getter?

Question

Consider the following example:

class A:
    @property
    def x(self): return 5

So, of course calling the a = A(); a.x will retur

Answer 1

I just ran into this issue. I have class Polynomial() and I'm defining a gradient that I would like to return a function if no arguments or evaluate if there are arguments. I want to store the gradient as an attribute so I don't need to calculate it every time I need to use it, and I want to use @property so the gradient attribute is calculated lazily. My solution was to define a class Gradient with a defined call method for Polynomial's grad property to return.

@property
def grad(self):
    """
    returns gradient vector
    """
    class Gradient(list):
        def __call__(self, *args, **kwargs):
            res = []
            for partial_derivative in g:
                res.append(partial_derivative(*args, **kwargs))
            return res
    g = Gradient()
    for i in range(1, len(self.term_matrix[0])):
        g.append(self.derivative(self.term_matrix[0][i]))
    return g

And then I have the following tests pass successfully:

def test_gradient(self):
    f = Polynomial('x^2y + y^3 + xy^3')
    self.assertEqual(f.grad, [Polynomial('2xy + y^3'), Polynomial('x^2 + 3xy^2 + 3y^2')])
    self.assertEqual(f.grad(x=1, y=2), [12, 25])
    f = Polynomial('x^2')
    self.assertEqual(f.grad(1), [2])

So, for this issue we could try:

class A:
    @property
    def x(self):
        class ReturnClass(int):
            def __call__(self, neg=False):
                if not neg:
                    return 5
                return -5
        return ReturnClass()