Why are these 2 python class instance could equal to each other?

Question

from dataclasses import dataclass

@dataclass
class ThreeDPoint:
    x: int | float
    y = 0.0
    z: int | float = 0.0

point_1 = ThreeDPoint(1.0,2)

point_3 = ThreeDPoint(1,2)
print(point_1 == point_3)

The result is true.

I ran it in python playground. The result said it is true. I think this dataclass module might play some magic trick inside but I am not sure what is exactly happening.

Answer 1

There is no magic trick. In Python, integer 1 and float 1.0 are the same

> 1 == 1.0
True

On the other hand, type(1) is not the same as type(1.0)

> type(1) == type(1.0)
False

If you would like the equality operator to behave the way you suggested (= returning False when x has the same value but different type), then you could define your own equality method for the class, like so:

from dataclasses import dataclass


@dataclass
class ThreeDPoint:
    x: int | float
    y = 0.0
    z: int | float = 0.0

    def __eq__(self, other):
        for var, var_value in self.__dict__.items():
            try:
                other_var_value = getattr(other, var)
                if not (var_value == other_var_value and type(var_value) is type(other_var_value)):
                    return False
            except AttributeError:
                return False
        return True


point_1 = ThreeDPoint(1.0, 2)
point_3 = ThreeDPoint(1, 2)
print(point_1 == point_3)