How do you modify this code so that it will print the input string in reversed order?

Question

I have this code and I don't why it doesn't print the input string in reversed order. I have specified it to print from the last character of the string to the first character with (-1,0,-1).

string=str(input())

for i in range(-1,0,-1):
    print(string[i],end="")

Duplicate question of https://stackoverflow.com/questions/931092/reverse-a-string-in-python — cylee, Oct 02 '18 at 18:17
I modified it to range(len(string)-1,0,-1): but the first character is still missing — Yolanda Hui, Oct 02 '18 at 18:17
@YolandaHui: that's because the second parameter is *exclusive*, so you should use `-1`. — Willem Van Onsem, Oct 02 '18 at 18:18
@YolandaHui try `range(len(string)-1, -1, -1)`. The last element of the range is never included, so the zero-index character won't be included — Joel, Oct 02 '18 at 18:18
Possible duplicate of [Reverse a string in Python](https://stackoverflow.com/questions/931092/reverse-a-string-in-python) — Aaron, Oct 02 '18 at 18:21

Willem Van Onsem · Accepted Answer · 2018-10-02T18:20:57.213

The range(-1, 0, -1) is empty. A range can not work with the fact that -1 will result in the last element, since it does not know the length of the collection (here a string).

So if we convert the range(..) to a list, we get:

>>> list(range(-1, 0, -1))
[]

You thus need to start with len(string)-1, furthermore since the second parameter is exclusive, this should be -1. For example:

>>> string = 'foobar'
>>> list(range(len(string)-1, -1, -1))
[5, 4, 3, 2, 1, 0]

So in your case we can use this like:

for i in range(len(string)-1, -1, -1):
    print(string[i],end="")

An aternative is to use reversed(..), or by slcing the string:

for c in reversed(string):
    print(c, end='')

Note that you better first generate the full string, so for example:

print(string[::-1])

or an alternative (but less performant):

print(''.join(reversed(string))

Thanks I learned how to use reversed now, it looks like its the best way to do it. — Yolanda Hui, Oct 02 '18 at 18:20

score 2 · Answer 2 · answered Oct 02 '18 at 18:17

2

Use slice notation to print the string backwards:

print(string[::-1])

The -1 is the step size and direction.

answered Oct 02 '18 at 18:17

figbeam

7,001
2
12
18

score 2 · Answer 3 · answered Oct 02 '18 at 18:17

2

As Willem Van Onsem pointed out, range(-1, 0, 1) is empty. If you're looking to print a string in reversed order, it's easier to use string slicing:

print(string[::-1])

answered Oct 02 '18 at 18:17

Joel

1,564
7
12
20

score 2 · Answer 4 · answered Oct 02 '18 at 18:20

2

Your range is not defined correctly, as demonstrated by:

for i in range(-1,0,-1):
  print(i)

doesn't return anything. Moreover len(i) returns 0.

Just use list extended syntax here:

string=str(input())
print(string[::-1])

answered Oct 02 '18 at 18:20

jeannej

1,135
1
9
23

Small error: the second parameter should be `-1`, not `0`. – Willem Van Onsem Oct 02 '18 at 18:21
you mean in 'range' ? I just took what was in the original question to show that it doesn't work – jeannej Oct 02 '18 at 18:23
Ah, sorry, did not got that somehow. +1. – Willem Van Onsem Oct 02 '18 at 18:24

How do you modify this code so that it will print the input string in reversed order?

4 Answers4