This likely comes from the fact that .x originates in Tk directly, but .y must be inverted (by subtracting from canvas height) to be consistent with the canvas. I'm not sure if this is a bug though; the documentation simply states that they are scalars, which doesn't really commit either way.

Is there any reason we can't cast to an int before y is returned if it is always integer valued?

Probably not, but I suppose that theoretically you could get half-pixels on something like a HiDPI screen. But I don't know this for sure, and the docs never really made a commitment either way.

At least the qt5 backend returns physical pixels here (we perform an explicit conversion in mouseEventCoords, so they should always be possible to return integers (which seems indeed better?).
On the other hand, the tk backend doesn't really support retina (#10388), so I'm not sure what's the exact situation there...

(actually all backends currently share the inconsistency of returning x as int and y as float, so removed the tk label)

Lets cast y to be an int every where.

I can submit a PR

Thanks @TarasKuzyo ! Please make sure you get all of the backends

I was thinking of casting x and y to int in LocationEvent's constructor, from which MouseEvent inherits. In such a way it will be backend-independent solution.

It would also be useful to specify the types of x and y in the documentation.

Fixed by #11530.