Insert a string before a substring of a string

Question

I want to insert some text before a substring in a string.

For example:

str = "thisissometextthatiwrote"
substr = "text"
inserttxt = "XX"

I want:

str = "thisissomeXXtextthatiwrote"

Assuming substr can only appear once in str, how can I achieve this result? Is there some simple way to do this?

Take a look at this answer http://stackoverflow.com/a/24450558/1326943 — CJ4, May 14 '15 at 08:11
possible duplicate of [how to insert some string in the given string at given index in python](http://stackoverflow.com/questions/4022827/how-to-insert-some-string-in-the-given-string-at-given-index-in-python) — Dhinakaran Thennarasu, May 14 '15 at 08:14
@DhinakaranThennarasu it's not a dupe of that one, because that one doesn't ask how to find the index of substr — GreenAsJade, May 14 '15 at 09:31

score 26 · Accepted Answer · answered May 14 '15 at 08:11

26

my_str = "thisissometextthatiwrote"
substr = "text"
inserttxt = "XX"

idx = my_str.index(substr)
my_str = my_str[:idx] + inserttxt + my_str[idx:]

ps: avoid using reserved words (i.e. str in your case) as variable names

answered May 14 '15 at 08:11

Dušan Maďar

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score 16 · Answer 2 · answered Apr 02 '19 at 00:09

16

Why not use replace?

my_str = "thisissometextthatiwrote"
substr = "text"
inserttxt = "XX"

my_str.replace(substr, substr + inserttxt)
# 'thisissometextXXthatiwrote'

answered Apr 02 '19 at 00:09

santon

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In Python .replace() returns a copy of string, so I guess it should be: `new_str = my_str.replace(substr, substr + inserttxt)` – Andrey Sherman Jul 23 '20 at 08:52
This is confusing it replaces `text` with `textXX` – alper Jun 03 '21 at 13:47

lord63. j · Answer 3 · 2015-05-21T02:33:52.507

9

Use str.split(substr) to split str to ['thisissome', 'thatiwrote'], since you want to insert some text before a substring, so we join them with "XXtext" ((inserttxt+substr)).

so the final solution should be:

>>>(inserttxt+substr).join(str.split(substr))
'thisissomeXXtextthatiwrote'

if you want to append some text after a substring, just replace with:

>>>(substr+appendtxt).join(str.split(substr))
'thisissometextXXthatiwrote'

edited May 21 '15 at 02:33

answered May 14 '15 at 08:15

lord63. j

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could you add an explanation? – Robert May 14 '15 at 08:19
2

@Robert using `str.split(substr)` to split `str` to `['thisissome', 'thatiwrote']`, and then we join them with "XXtext" (`(inserttxt+substr)`). – lord63. j May 14 '15 at 08:30

score 0 · Answer 4 · edited Aug 25 '18 at 09:28

0

With respect to the question (were ´my_str´ is the variable), the right is:

(inserttxt+substr).join(**my_str**.split(substr))

edited Aug 25 '18 at 09:28

glennsl

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answered Aug 25 '18 at 09:04

Daniela Mazza

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Insert a string before a substring of a string

4 Answers4