How to replace characters in a string which we know the exact indexes in python?
Ex : name = "ABCDEFGH" I need to change all odd index positions characters into '$' character.
name = "A$C$E$G$" (Considered indexes bigin from 0 )
4 Answers
Also '$'.join(s[::2]) Just takes even letters, casts them to a list of chars and then interleaves $
''.join(['$' if i in idx else s[i] for i in range(len(s))]) works for any index array idx
6 Comments
TigerhawkT3
You don't even need the
list() call. :)
Kasravnd
Question is based on the indices so this is not a proper way!
Duncan
In general for this sort of manipulation, convert to a list, manipulate the indices in the list then join back to a string, but in this specific example as you showed it collapses down beautifully into a join and slice with skip.
TigerhawkT3
@Kasramvd, it's an XY Problem.
Kasravnd
@TigerhawkT3 Yeah a sort of! but not completely!
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You can use enumerate to loop over the string and get the indices in each iteration then based your logic you can keep the proper elements :
>>> ''.join([j if i%2==0 else '$' for i,j in enumerate(name)]) 'A$C$E$G$' 1 Comment
TigerhawkT3
You could shorten this slightly with
'$' if i%2 else j.name = "ABCDEFGH" nameL = list(name) for i in range(len(nameL)): if i%2==1: nameL[i] = '$' name = ''.join(nameL) print(name) 
Comments
You can reference string elements by index and form a new string. Something like this should work:
startingstring = 'mylittlestring' nstr = '' for i in range(0,len(startingstring)): if i % 2 == 0: nstr += startingstring[i] else: nstr += '$' Then do with nstr as you like.
6 Comments
cdarke
The reason why the other solutions use a list with
join is to avoid this - you are creating a new string object each time you use +=.
Andrew
I did not know that. I figured it was, in effect, appended to an existing string. What's the detail of the operation? Does it (1) create a new string consisting of the old
nstr concatenated with the new character, (2) delete the old nstr and (3) move the new string to nstr?TigerhawkT3
You can't append to an existing string because strings are immutable in Python.
cdarke
Just about, yes. Python is not the only language like this, PHP and Java are examples that are the same. Perl is the odd one out (in so many ways).
Andrew
Good to know. Thanks for the post.
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