How to substitute character in string using regex

Question

I want to change the following string

^mylog\.20151204\-\d{2}\:\d{2}\:\d{2}\.gc\.log\.gz$

to this:

^mylog\.2015-12-04\-\d{2}\:\d{2}\:\d{2}\.gc\.log\.gz$

(20151204 changed to 2015-12-04 only)

I can accomplish it by:

re.sub("20151204", "2015-12-04", string)

where

string= ^mylog\.20151204\-\d{2}\:\d{2}\:\d{2}\.gc\.log\.gz$

But the value 20151204 is a date and will change and I can't have it hardcoded.

I tried:

re.sub("2015\\d{2}\\d{2}", "2015\-\\d{2}\-\\d{2}", string)

However this did not work.

Wiktor Stribiżew · Accepted Answer · 2015-12-09 10:56:45Z

1

You need to use capture groups in the pattern and backreferences in the replacement:

result = re.sub("2015(\\d{2})(\\d{2})", "2015-\\1-\\2", string)
                     ^      ^^      ^         ^^^ ^^^   
// => ^mylog\.2015-12-04\-\d{2}\:\d{2}\:\d{2}\.gc\.log\.gz$

See IDEONE demo

If you need to match any year after ^mylog\., you can use

result = re.sub(r"^\^mylog\\\.(\d{4})(\d{2})(\d{2})", r"^mylog\.\1-\2-\3", string)

See another demo

answered Dec 9, 2015 at 10:56

Wiktor Stribiżew

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Rohan Amrute · Accepted Answer · 2015-12-09 11:10:42Z

0

You first need to find the date and then convert it into the required format and then replace the new string in your old text.

See the code below:

 text = "^mylog\.20151204\-\d{2}\:\d{2}\:\d{2}\.gc\.log\.gz$"
 search = re.search(r'\d{4}\d{2}\d{2}',text)
 search = search.group()

you get search as:

20151204

Now create the date as you want:

 new_text = search[0:4] + "-" + search[4:6] + "-" + search[6:8]

So new_text will be:

2015-12-04

Now substitute this new_text in place of the earlier string using `re.sub()

  text = re.sub(search,new_text,text)

So now text will be:

^mylog\.2015-12-04\-\d{2}\:\d{2}\:\d{2}\.gc\.log\.gz$

answered Dec 9, 2015 at 11:10

Rohan Amrute

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