Python expm1(x) function returns the natural exponential value of x minus 1. It is equal to math.e**x - 1. It's a method of math module.

>>> import math
>>> math.expml(2)

6.38905609893065

>>> math.e**2 - 1

6.38905609893065

>>> math.expml(3)

19.085536923187668

>>> math.expml(4)

53.598150033144236