How to solve invalid syntax error in a simple if else statement in Python?

I'm in the middle of creating an autocorrelation code and just doesn't work. It is simple but I'm stuck and have no idea how to fix this code.

S1 = [1, 0, 1, 0, 0, 1]

func = 0;
for l in range(0,254):
  for i in range (0,254):
    if int(l+i) < 255:
      func = (1-2*S1[i])*(1-2*(S1[i+l])
    else :
      func = (1-2*S1[i])*(1-2*(S1[(i+l)%2])
  if func = 255 or 1 or -1
    print ("R(%s) = %s " %l, %func)

There's a problem with the else statement but I'm not sure exactly what I did wrong.

Can you help me out?