python re.sub, only replace part of match

Question

I am very new to python

I need to match all cases by one regex expression and do a replacement. this is a sample substring --> desired result:

<cross_sell id="123" sell_type="456"> --> <cross_sell>

i am trying to do this in my code:

myString = re.sub(r'\<[A-Za-z0-9_]+(\s[A-Za-z0-9_="\s]+)', "", myString)

instead of replacing everything after <cross_sell, it replaces everything and just returns '>'

is there a way for re.sub to replace only the capturing group instead of the entire pattern?

what if i want my output as i.e i want to replace cross_cell with mystring — Kshitij Agrawal, Jul 12 '20 at 10:31

score 27 · Accepted Answer · answered Sep 21 '15 at 15:11

27

You can use substitution groups:

>>> my_string = '<cross_sell id="123" sell_type="456"> --> <cross_sell>'
>>> re.sub(r'(\<[A-Za-z0-9_]+)(\s[A-Za-z0-9_="\s]+)', r"\1", my_string)
'<cross_sell> --> <cross_sell>'

Notice I put the first group (the one you want to keep) in parenthesis and then I kept that in the output by using the "\1" modifier (first group) in the replacement string.

answered Sep 21 '15 at 15:11

mgilson

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beautiful answer! – vagabond Jan 10 '20 at 23:01
what if i want my output as i.e i want to replace cross_cell with mystring – Kshitij Agrawal Jul 12 '20 at 10:33

Mazdak · Answer 2 · 2015-09-21T15:21:52.093

3

You can use a group reference to match the first word and a negated character class to match the rest of the string between <> :

>>> s='<cross_sell id="123" sell_type="456">'
>>> re.sub(r'(\w+)[^>]+',r'\1',s)
'<cross_sell>'

\w is equal to [A-Za-z0-9_].

edited Sep 21 '15 at 15:21

answered Sep 21 '15 at 15:11

Mazdak

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Good call on the `\w+`. – mgilson Sep 21 '15 at 15:13
Couldn't it be simplified to `re.sub(r'(\w+)[^>]+',r'\1',s)`? – Lucas Infante Sep 21 '15 at 15:19
@maccinza Indeed, nice! – Mazdak Sep 21 '15 at 15:22
@maccinza -- For the input text, it can be simplified ... However, I'm not sure you would want to make that substitution in general... (who knows what the content of the tag looks like?) – mgilson Sep 21 '15 at 16:00

score 1 · Answer 3 · answered Sep 21 '15 at 15:24

Since the input data is XML, you'd better parse it with an XML parser.

Built-in xml.etree.ElementTree is one option:

>>> import xml.etree.ElementTree as ET
>>> data = '<cross_sell id="123" sell_type="456"></cross_sell>'
>>> cross_sell = ET.fromstring(data)
>>> cross_sell.attrib = {}
>>> ET.tostring(cross_sell)
'<cross_sell />'

lxml.etree is an another option.

score 1 · Answer 4 · answered Jun 01 '17 at 03:25

1

below code tested under python 3.6 , without use group..

test = '<cross_sell id="123" sell_type="456">'
resp = re.sub(r'\w+="\w+"' ,r'',test)
print (resp)

<cross_sell>

answered Jun 01 '17 at 03:25

xiyurui

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python re.sub, only replace part of match

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