How does iteration work in function

How does iteration work in function

here's my problem. Sorry for the previous post which was not clear at all.
so here's an example :
import numpy as np
x=np.arange(1,100,1)
y=z=x*0
def func(h,g):
for i in range(1,50):
h[i]=i+1
g[i]=i*2
func(z,y)
print z-y
In this example z and y give the same answer but why is that so? in the
function it is not supose to give the same answer?