Question

I want to make ‘==’ operator use approximate comparison in my program: float values x and y are equal (==) if

abs(x-y)/(0.5(x+y)) < 0.001

What’s a good way to do that? Given that float is a built-in type, I don’t think I can redefine the == operator, can I?

Note that I would like to use other features of float, the only thing that I’d like to change is the equality operator.

EDIT:

Thank you for the answers, and I understand your arguments about readability and other issues.

That said, I really would prefer, if possible, to actually keep using the regular float type, instead of having a new class or a new comparison function. Is it even possible to redefine == operator for regular floats?

My reasons are::

(a) everyone using the program I’m writing wants the floats to be compared this way

(b) there’s no way in the world anyone would ever want to use the default == for floats.. Why is it even in the language???

(c) I dislike extra words in the code; obviously using the existing float results in no changes in the code whatsoever

EDIT 2.

Now that I know I can’t overload the == operator for float, I have to change my question. It will become so different that I’ll make a new one at custom comparison for built-in containers

Answer 1

Your definition has two problems:

1. Missing an *

2. Will attempt to divide by zero if x + y == 0.0 (which covers a possibly frequent case x == y == 0.0)

Try this instead:

define approx_Equal(x, y, tolerance=0.001):
    return abs(x-y) <= 0.5 * tolerance * (x + y)

Edit: Note the use of <= instead of < … needed to make the x == y == 0.0 case work properly.

I wouldn’t try to override ==

Edit 2: You wrote:

there’s no way in the world anyone would ever want to use the default
== for floats.. Why is it even in the language???

No way? Suppose you have a function that returns a float, and you have a brainwave about an algorithm that would produce the same answers faster and/or more elegantly; how do you test it?