CODEWITHSUNDEEP
pythonregex
killajoule
killajoule

Reputation: 3832

Python - Replace part of regex?

I have the following piece of code:

import re
s = "Example {String}"
replaced = re.sub('{.*?}', 'a', s)
print replaced

Which prints:

Example a

Is there a way to modify the regex so that it prints:

Example {a}

That is I would like to replace only the .* part and keep all the surrounding characters. However, I need the surrounding characters to define my regex. Is this possible?

Upvotes: 2

Views: 289

Answers (1)

Adam Smith
Adam Smith

Reputation: 54243

Two ways to do this, either capture your pre- and post-fixes, or use lookbehinds and lookaheads.

# capture
s = "Example {String}"
replaced = re.sub(r'({).*?(})', r'\1a\2', s)

# lookaround
s = "Example {String}"
replaced = re.sub(r'(?<={).*?(?=})', r'a', s)

If you capture you pre- and post-fixes, you're able to use those capture groups in your substitution using \{capture_num}, e.g. \1 and \2.

If you use lookarounds, you essentially DON'T MATCH those pre-/post-fixes, you simply assert that they are there. Thus the substitution only swaps the letters in between.

Of course for this simple sub, the better solution is probably:

re.sub(r'{.*?}', r'{a}', s)

Upvotes: 5

Related Questions