python - UnboundLocalError at inversing a string

def FirstReverse(str):


    chaine = str.split(' ');

     for i in range(len(chaine), -1):
       inverse = chaine[i]
   return inverse ;    


print FirstReverse(raw_input())

i want to inverse a string but i have some difficulties , i got this error message

UnboundLocalError: local variable 'inverser' referenced before assignment