od0o  = np.zeros((N,))
od0o[0]=0.7
od0n = np.zeros((N,))

def TOTAL(a):
...
   return...

for i in range (1,N):
   R = np.random.uniform(0,1)

   od0n[i] = od0o[i-1] + 0.001 * np.random.normal()

   L = np.exp(-0.5 * (TOTAL(od0n[i]) - TOTAL(od0o[i-1]))
   LL=min(1,max(L,0))

   if LL>R:
        od0o[i]= od0n[i]
        chi = TOTAL(od0o[i])
   else:
        od0o[i]= od0o[i-1]
        chi = TOTAL(od0o[i])