how good is the optimization?

[Skaperen]

how good is the optimization in Python? in this code will it cache the value from s[n] or will it fetch it twice?

   if s[n]<128 or s[n]>191:
        return -2

or should i code this?

    x = s[n]
    if x<128 or x>191:
        return -2

for best performance.