Cast a Python class to Numpy Array

Question

Can I cast a python class to a numpy array?

from dataclasses import dataclass
import numpy as np
@dataclass
class X:
    x: float = 0
    y: float = 0
x = X()
x_array = np.array(x) # would like to get an numpy array np.array([X.x,X.y])

In the last step, I would like the to obtain an array np.array([X.x, X.y]). Instead, I get array(X(x=0, y=0), dtype=object).

Can I provide method for the dataclass so that the casting works as desired (or overload one of the existing methods of the dataclass)?

try to add def __iter__(self): yield from (self.x, self.y) — Azat Ibrakov
– Azat Ibrakov, Commented Nov 30, 2020 at 9:00
Thanks for your suggestion @AzatIbrakov ! I did try but to no avail. Maybe I defined it the wrong way. Can you provide a fully specified answer? — fabian
– fabian, Commented Nov 30, 2020 at 9:07
it was a wrong suggestion based only on intuition, after reading a docstring of numpy.array it is clear that you can define __array__ method like def __array__(self): return np.array([self.x, self.y]) — Azat Ibrakov
– Azat Ibrakov, Commented Nov 30, 2020 at 9:19
Thanks @AzatIbrakov ! This is really helpful. Do you want to write an answer so that I can accept? — fabian
– fabian, Commented Nov 30, 2020 at 9:25

Azat Ibrakov · Accepted Answer · 2021-04-28 08:21:39Z

8

From docstring of numpy.array we can see requirements for the first parameter

object: array_like

An array, any object exposing the array interface, an object whose __array__ method returns an array, or any (nested) sequence.

So we can define an __array__ method like

@dataclass
class X:
    x: float = 0
    y: float = 0

    def __array__(self) -> np.ndarray:
        return np.array([self.x, self.y])

and it will be used by np.array. This should work for any custom Python class I guess.

edited Apr 28, 2021 at 8:21

answered Nov 30, 2020 at 9:33

Azat Ibrakov

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