How to substitute correctly in python using regex

Question

I have a python string:

s = 'filename               13.00 50850.8732503344475    37.11  abc'

In order to find the second string with format nn.nn, I know I can do:

re.findall(r'.*(\b\d+\.\d+)',s)[0]

which finds:

'37.11'

But I want to replace it with 99.99.

I tried:

re.sub(r'.*(\b\d+\.\d+)','99.99',s)

But that just yields:

'99.99  abc'

whereas I want:

'filename               13.00 50850.8732503344475    99.99  abc'

Clearly I don't yet understand how regex works. Could someone offer help please?

Wiktor Stribiżew · Accepted Answer · 2019-08-26 21:35:05Z

2

You should capture what you need to keep and use the unambiguous replaement backreference in the replacement pattern:

s = re.sub(r'(.*)\b\d+\.\d+',r'\g<1>99.99', s)

See the Python demo and the regex demo.

Pattern details

(.*) - Group 1 (its value is referred to with \g<1> backreference from the replacement pattern): any 0+ chars other than line break chars as many as possible
\b - a word boundary
\d+ - 1+ digits
\. - a dot
\d+ - 1+ digits.

answered Aug 26, 2019 at 21:35

Wiktor Stribiżew

631k41 gold badges502 silver badges632 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Olvin Roght · Accepted Answer · 2019-08-26 22:00:17Z

1

Alternatively, you can replace last occurrence of simple pattern (\d+\.\d+):

s = "filename               13.00 50850.8732503344475    37.11  abc"
*_, last = re.finditer(r"(\d+\.\d+)", s)
s = s[:last.start()] + "99.99" + s[last.end():]

It's a bit faster. Results of timeit benchmark(code):

re.finditer() -> 11.30306268
re.sub() -> 15.613837582000002

edited Aug 26, 2019 at 22:00

answered Aug 26, 2019 at 21:51

Olvin Roght

7,8432 gold badges19 silver badges39 bronze badges

Collectives™ on Stack Overflow

How to substitute correctly in python using regex

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related