Python 3.9+Numbers & mathfunction

math.nextafter

representation

The next representable float after x toward y.

Syntax

math.nextafter(...)

Added in Python 3.9; the steps argument only arrived in 3.12. It is the tool for nudging a bound by the smallest possible amount — building a half-open float range, or checking whether two floats are adjacent with nothing representable in between. When x equals y the result is y, and nextafter(0.0, 1.0) returns the smallest positive subnormal, 5e-324.

Examples

import math
print(math.nextafter(1.0, 2.0))   # → 1.0000000000000002
print(math.nextafter(1.0, 0.0))   # → 0.9999999999999999
print(math.nextafter(0.0, 1.0))   # → 5e-324
print(math.nextafter(2.0, 2.0))   # → 2.0

# Python 3.12+
import math
print(math.nextafter(1.0, 2.0, steps=2))   # → 1.0000000000000004

See also

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