Find maximum and minimum of a scalar field

How do I set the array equal to the expression you wrote?
I have this that gives me the Helicity array which i need to normalize:

calculator1 = Calculator(Input=openFOAMReader2)
calculator1.ResultArrayName = 'Helicity'
calculator1.Function = '(U_X*vorticity_X+U_Y*vorticity_Y+U_Z*vorticity_Z)/(sqrt(U_X^2+U_Y^2+U_Z^2+vorticity_X^2+vorticity_Y^2+vorticity_Z^2)'

What should i set equal to this code you wrote?

Thanks for all the help, i’m not very good at python