UnboundLocalError at inversing a string

Question

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

Answer 1

You need to pass a negative step argument to range to get a reversed range list.

range(len(chaine)-1, -1, -1)   #start from len(chaine)-1

As because range(len(chaine), -1) returns [], the loop never executes and inverse never gets defined.

Easiest way to inverse a string is to use the extended slice notation [::-1].

Answer 2

Your for statement is always false and inverse gets initialized only if for loop condition is met, so the code doesn't reach the point where inverse gets a value (and by that, gets defined/bound). You should introduce the variable in a place that always gets executed.

Answer 3

A better way to reverse a list is to use slice notation with a step of -1:

def FirstReverse(s):
    words = s.split(' ')
    return words[::-1]

Notes:

1. str is a Python built-in, avoid re-using it
2. You don't need to finish statements with semicolons;