regex and replace on string using python

Question

I am rather new to Python Regex (regex in general) and I have been encountering a problem. So, I have a few strings like so:

str1 = r'''hfo/gfbi/mytag=a_17014b_82c'''
str2 = r'''/bkyhi/oiukj/game/?mytag=a_17014b_82c&'''
str3 = r'''lkjsd/image/game/mytag=a_17014b_82c$'''

the & and the $ could be any symbol.

I would like to have a single regex (and replace) which replaces:

mytag=a_17014b_82c

to:

mytag=myvalue

from any of the above 3 strings. Would appreciate any guidance on how I can achieve this.

UPDATE: the string to be replaced is always not the same. So, a_17014b_82c could be anything in reality.

Is the string to be replaced always the same? In that case, you don't need a regex. — keyser
– keyser, Commented Aug 4, 2013 at 13:40
if these are url's as they appear to be, the & has special meaning so your statement that "the & and the $ could be any symbol" feels wrong. — Phil Cooper
– Phil Cooper, Commented Aug 4, 2013 at 13:43
I would want it to always replace the value of mytag - if this makes sense. i.e mytag will always be present in the string. — JohnJ
– JohnJ, Commented Aug 4, 2013 at 13:47

keyser · Accepted Answer · 2013-08-04 13:42:46Z

1

If the string to be replaced is constant you don't need a regex. Simply use replace:

>>> str1 = r'''hfo/gfbi/mytag=a_17014b_82c'''
>>> str1.replace('a_17014b_82c','myvalue')
'hfo/gfbi/mytag=myvalue'

answered Aug 4, 2013 at 13:42

keyser

19.3k16 gold badges62 silver badges103 bronze badges

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

1 Comment

JohnJ Over a year ago

Just posted an update - sorry, the string to be replaced is always not the same. Sorry for not being clear the first time around.

Ashwini Chaudhary · Accepted Answer · 2013-08-04 13:48:36Z

1

Use re.sub:

>>> import re
>>> r = re.compile(r'(mytag=)(\w+)')
>>> r.sub(r'\1myvalue', str1)
'hfo/gfbi/mytag=myvalue'
>>> r.sub(r'\1myvalue', str2)
'/bkyhi/oiukj/game/?mytag=myvalue&'
>>> r.sub(r'\1myvalue', str3)
'lkjsd/image/game/mytag=myvalue$'

answered Aug 4, 2013 at 13:48

Ashwini Chaudhary

252k60 gold badges478 silver badges519 bronze badges

3 Comments

JohnJ Over a year ago

@Ashwini: This is awesome. Could you please explain why you use \1?

Ashwini Chaudhary Over a year ago

@JohnJ \1 represents the first matching group i.e 'mytag='.

JohnJ Over a year ago

@AshwiniChaudhary: Thank you very much for your explanation. Accepted your answer! Was breaking my head over this for a couple of hours. Thanks again.

Sundar R · Accepted Answer · 2013-08-04 14:04:47Z

0

import re
r = re.compile(r'(mytag=)\w+$')
r.sub(r'\1myvalue', str1)

This is based on @Ashwini's answer, two small changes are we are saying the mytag=a_17014b part should be at the end of input, so that even inputs such as

str1 = r'''/bkyhi/mytag=blah/game/?mytag=a_17014b_82c&'''

will work fine, substituting the last mytag instead of the the first.

Another small change is we are not unnecessarily capturing the \w+, since we aren't using it anyway. This is just for a bit of code clarity.

answered Aug 4, 2013 at 14:04

Sundar R

14.8k7 gold badges56 silver badges80 bronze badges

Collectives™ on Stack Overflow

regex and replace on string using python

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related