Trying to reverse a string by prepending characters

Question

I am working on a function to reverse a string and when I run it I get two errors, one at tot -= i showing TypeError: unsupported operand type(s) for -=: 'str' and 'str', and at print(reverse(thestr)).

However, if I put the + in tot += i, it works. How can I solve this, as for my understanding when using - it will go in reverse?

def reverse(c):
    tot = ''
    for i in c:
        tot -= i
    return tot
thestr = 'This is a Test'
print(reverse(thestr))

The `-` operator is not defined for strings. It's a nice idea to think that `tot -= i` adds `i` to the left of `tot`, but that's not how it works. — mkrieger1, Nov 27 '20 at 00:47
Maybe you should add `tot` to the right of `i` and assign this back to `tot`? — mkrieger1, Nov 27 '20 at 00:48
Does this answer your question? [Prepend text to beginning of string](https://stackoverflow.com/questions/6094117/prepend-text-to-beginning-of-string) (oops that's JavaScript, but the answer is the same...) — mkrieger1, Nov 27 '20 at 00:50
"as for my understanding the use the - it will go in reverse" no, that isn't the case, as the error indictes — juanpa.arrivillaga, Nov 27 '20 at 00:50

wjandrea · Accepted Answer · 2020-11-27T01:04:02.097

1

for my understanding the use the - it will go in reverse

That's incorrect.

To prepend, you can do this:

tot = i + tot

Or, to solve the problem more pythonically, use reversed():

def reverse(c):
    tot = ''
    for i in reversed(c):
        tot += i
    return tot

Which can then be simplified with ''.join():

def reverse(c):
    return ''.join(reversed(c))

Or simply use a reverse slice:

def reverse(c):
    return c[::-1]

edited Nov 27 '20 at 01:04

answered Nov 27 '20 at 00:54

wjandrea

28,235
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The "pythonic" way to reverse a string would be simply `return s[::-1]` which you might as well use if you are going to use `reversed` – juanpa.arrivillaga Nov 27 '20 at 01:02
@juanpa Oh yeah, I forgot about that, lol. Added, thanks – wjandrea Nov 27 '20 at 01:04
Thank you for the information. I am learning alot from all of you. Thanks – GiddyHeaD Nov 27 '20 at 01:12

score 0 · Answer 2 · answered Nov 27 '20 at 00:54

0

your code doesn't reverse a string. this will:

def reverse(c):
    l = len(c)
    tot = ''
    for i in range(l):
        tot += c[l - i - 1]
    return tot
thestr ='This is a Test'
print(reverse(thestr))

answered Nov 27 '20 at 00:54

0xedb

354
2
8

1

It's a bit simpler to do `for i in reversed(range(len(c))): tot += c[i]`, but there's no point using indices when you could just do `for i in reversed(c): tot += i` like I wrote in [my answer](https://stackoverflow.com/a/65030871/4518341). – wjandrea Nov 27 '20 at 01:06
using indices is a better place to start IMO. a beginner may be confused how `reversed` works – 0xedb Nov 27 '20 at 01:17

Trying to reverse a string by prepending characters

2 Answers2