Why This doesn't work?

Question

This code checks for palindrome
if yes, NULL is printed
if no, characters to be added to make it palindrome is printed

if input = malay, output = alam
but, if input = abcdc, output = dba why?

https://code.sololearn.com/cc9nRCXm3yYC/?ref=app

Answer 1

Simple without loops

msg = input( 'enter: ' )
rev_msg = msg[ : : -1 ]
if msg == rev_msg:
print( 'NULL' )
else:
print( rev_msg[ 1 : ] )

Answer 2

thanks for your code

Answer 3

and the code was written by me

Answer 4

Harsha S because in print you print null

Answer 5

no, i understand what rev_msg[1:] is
it's list slicing

i meant why rev_msg[1:]?

Answer 6

oh ok

say, maam is palindrome
but if i input "ma", i get "m" as output

how do i make it to get output as "am"?

Answer 7

"But if I input 'ma', I get 'm' as output"
Yes, because 'ma' + 'm' -> 'mam' is palindrome.

To get 'am' simply don't slice, print( rev_msg ) rather than print( rev_msg[ 1 : ] ).

But this way we have twin character at the center.

(Edit)
You can also take length of <msg> as consideration. If length of <msg> was odd, slice <rev_msg>, otherwise don't slice.

Answer 8

thank you

Answer 9

Yes, the code is right but your output is not dba, it's dcba

Answer 10

Sabarinathan.M

i've corrected the error already 😁

Answer 11

Calvin Thomas a for abcdcb

Answer 12

No problem, but do you understand how it works? copy/paste is easy, but to understand it is better.

Answer 13

yeah, why rev_msg[1:]?

Answer 14

not copied. yours was better so i took it

Answer 15

i'll Remove if you mind

Answer 16

No, I don't mind at all.
I meant to say, you can ask, in case there's something you don't clearly understand from the code I posted. It's important to understand.

rev_msg[ 1 : ] returns a slice of <rev_msg> from second character (index 1) up to the last.

Example:
msg = "abcdc"
rev_msg = "cdcba" # reversed
rev_msg[ 1 : ] = "dcba" # slice from second character

Answer 17

it was supposed to be
if msg[i] == msg[len(msg)-msg.index(i)]:

Answer 18

Because we want to append a reversed string <rev_msg> at the end of <msg> to make <msg> palindrome. But to achieve that, we skip the first character from <rev_msg> cause it will become the center character.

Answer 19

PARVIK PARASHAR

I need to print NULL if the input is already a palindrome

Answer 20

Harsha S What should be the output for 'abcdcb'?