There seemed to be a good amount of confusion in using accumulators to print out the reverse of a string. This combines a few advanced ideas so let us try to break it down into its pieces. First, when we accumulate a string, we are trying to "build up" the string piece by piece. In this case, we are trying to add one letter at a time from a string. The solution we had in class was:
reverse = ""
for i in range(len(word)-1, -1, -1):
    reverse += word[i]
print(reverse)
Let's step through this one iteration at a time. If we were to code this up without the loop, we can see what is happening at each iteration
#These are the initial steps
>>> word = "example"
>>> reverse = ""
>>> i = len(word)-1
>>> i
6
So our loop starts with i having the value len(word)-1, which is what we defined in our range function. Now we'll start accumulating:
>>> reverse += word[i] #add the last letter in the word as the first letter
                       # of reverse
>>> reverse
'e'
>>> i = i-1  #one iteration is done, move on to the next value
>>> i
5
>>> reverse += word[i]
>>> reverse
'el'
>>> i = i-1
>>> i
4
>>> reverse += word[i]
>>> reverse
'elp'
>>> i = i-1
>>> i
3
>>> reverse += word[i]
>>> reverse
'elpm'
>>> i = i-1
>>> i
2
>>> reverse += word[i]
>>> reverse
'elpma'
>>> i = i-1
>>> i
1
>>> reverse += word[i]
>>> reverse
'elpmax'
>>> i = i-1
>>> i
0
>>> reverse += word[i]
>>> i = i-1
>>> i
-1
Another solution to the problem constructs the loop in a more traditional way, but indexes differently:
reverse= ""
for i in range(1, len(word)+1):
    reverse += word[len(word)-1]
The loop looks different, but the accumulation is the same:
>>> word = "example"
>>> reverse = ""
>>> i = 1
>>> reverse += word[len(word)-i]
>>> reverse
'e'
>>> i=i+1
>>> reverse += word[len(word)-i]
>>> reverse
'el'
>>> i=i+1
>>> i
3
>>> reverse += word[len(word)-i]
>>> reverse
'elp'
>>> i=i+1
>>> i
4
>>> reverse += word[len(word)-i]
>>> reverse
'elpm'
>>> i=i+1
>>> i
5
>>> reverse += word[len(word)-i]
>>> reverse
'elpma'
>>> i=i+1
>>> i
6
>>> reverse += word[len(word)-i]
>>> reverse
'elpmax'
>>> i=i+1
>>> i
7
>>> reverse += word[len(word)-i]
>>> reverse
'elpmaxe'
>>> i=i+1
>>> i
8
>>>