import cmath def four(input): N=len(input) output=[0]*N for i in range(N): theta=2*cmath.pi*i/N expthetak=1.0 expthetal=cmath.exp(-1j*theta) for j in range(N): output[i]+=input[j]*expthetak expthetak*=expthetal return output def invfour(input): output=four([i.conjugate()/len(input) for i in input]) return [i.conjugate() for i in output] a=range(2000) b=range(2000) b.reverse() input=a+b print invfour(four(input))