Python copysign(x,y) function returns -x if y<0 and x if y>0. In other words, x copied the sign of y. It's a method of math module.

>>> import math
>>> math.copysign(0.2,-3)

-0.2

>>> math.copysign(0.2,-3)

0.2

>>> math.copysign(-54,3)

54.0

>>> math.copysign(-54,-3)

-54.0