Please help me!

Question

I have created this code for calculating a^n-b^n but I am getting wrong output:-
from sympy import *
a,b,z=symbols('a b z')
epn=lambda w,x,y: (w-x)*summation (w**(y-z)*x**z,(z,0,y-1))
print(epn(a,b,1/2).subs(a,4).subs(b,2))
print(epn(4,2,1/2))

Desired output:-0.58...
Getting output:-2.34....
2.34....

why is that happening?

Answer 1

try again with brackets for every operation , there's a lot going on in a single statement