Replace strings in a string by a substring of those strings

Question

Let's say I have a string like this:

s = '(X_xy09 and X_foobar or (X_abc123 and X_something))'

and I want to turn it into

'(xy09 and foobar or (abc123 and something))'

then - in this particular case - I could simply do

s.replace('X_', "")

which gives the desired output.

However, in my actual data there might be not only X_ but also other prefixes, so the above replace statement does not work.

What I would need instead is a replacement of

a capital letter followed by an underscore and an arbitrary sequence of letters and numbers

by

everything after the first underscore.

So, to extract the desired elements I could use:

import re
print(re.findall('[A-Z]{1}_[a-zA-Z0-9]+', s))

which prints

['X_xy09', 'X_foobar', 'X_abc123', 'X_something']

how can I now replace those elements so that I obtain

'(xy09 and foobar or (abc123 and something))'

?

Answer 1

If you need to remove an uppercase ASCII letter with an underscore after it, only when not preceded with a word char and when followed with an alphanumeric char, you may use

import re
s = '(X_xy09 and X_foobar or (X_abc123 and X_something))'
print(re.sub(r'\b[A-Z]_([a-zA-Z0-9])', r'\1', s))

See the Python demo and a regex demo.

Pattern details

• \b - a leading word boundary
• [A-Z]_ - an ASCII uppercase letter and _
• ([a-zA-Z0-9]) - Group 1 (later referenced to with \1 from the replacement pattern): 1 alphanumeric char.

Answer 2

If you just need to replace a capital letter followed by an underscore, you can use the regular expression r'[A-Z]_'.

s = '(X_xy09 and X_foobar or (X_abc123 and X_something))'
re.sub(r'[A-Z]_', '', s)

You may need to add to it if you have other criteria not mentioned. (For example, some of your target values follow a word boundary and some follow parentheses.) The above might give you the wrong output if you have input like XY_something. It depends on what you expect the output to be.