How can I force subtraction to be signed in Python?

You can skip to the bottom line if you don't care about the background:

I have the following code in Python:

ratio = (point.threshold - self.points[0].value) / (self.points[1].value - self.points[0].value)

Which is giving me wrong values. For instance, for:

threshold:  25.0
self.points[0].value:  46
self.points[1].value:  21

I got:

ratio:  -0.000320556853048

Which is wrong.

Looking into it, I realized that self.points[0].value and self.points[1].value] are of the typenumpy.uint16`, so I got:

21 - 46 = 65511

While I never defined a type for point.threshold. I just assigned it. I imagine it got a plain vanilla int.

The Bottom Line

How can I force the the subtraction of two uints to be signed?

Solution

Almost anything but uints will work here, so just cast these to something else before you do the subtraction.

Since threshold = 25.0 (note the decimal point), it's a float, so the subtraction and division will all work as long as you're not using uints.