Question

I want to match two regular expressions A and B where A and B appear as ‘AB’. I want to then insert a space between A and B so that it becomes ‘A B’.

For example, if A = [0-9] and B = !+, I want to do something like the following.

match = re.sub('[0-9]!+', '[0-9] !+', input_string)

But, this obviously does not work as this will replace any matches with a string ‘[0-9] !+’.

How do I do this in regular expressions (preferably in one line)? Or does this require several tedious steps?

Answer 1

Use the groups!

match = re.sub('([0-9])(!+)', r'\1 \2', input_string);

\1 and \2 indicate the first and second parenthesised fragment. The prefix r is used to keep the \ character intact.