["python"]
Increment a Python floating point value by the smallest possible amount

How can I increment a floating point value in python by the smallest possible amount? Background: I'm using floating point values as dictionary keys. Occasionally, very occasionally (and perhaps never, but not certainly never), there will be collisions. I would like to resolve these by incrementing the floating point value by as small an amount as possible. How can I do this? In C, I would twiddle the bits of the mantissa to achieve this, but I assume that isn't possible in Python.
Python 3.9 and above Starting with Python 3.9, released 2020-10-05, you can use the math.nextafter function: math.nextafter(x, y) Return the next floating-point value after x towards y. If x is equal to y, return y. Examples: math.nextafter(x, math.inf) goes up: towards positive infinity. math.nextafter(x, -math.inf) goes down: towards minus infinity. math.nextafter(x, 0.0) goes towards zero. math.nextafter(x, math.copysign(math.inf, x)) goes away from zero. See also math.ulp(). A simpler alternative to math.copysign(math.inf, x) is to simply substitute 2*x.