Python regex sub named captured

Question

I missing something very basic here.

I want to match all instances of, for instance, throw 'some string' or throw "error here".

p = re.compile(b'throw ["|\'](?P<err>).*["|\']')

This seems to work fine for matching. But, for instance, I want to replace throw 'some string' with, for instance, throw new Error('some string').

My attempt at this:

p.sub(rb"throw new Error('\g<err>')", b'throw \'foobar\'')

Always results in:

b"throw new Error('')"

I have found the match but replaced err with an empty string.

Answer 1

This matches and captures the empty string, followed by zero or more characters which are not captured:

(?P<err>).*

You want to move the .* inside the parentheses:

(?P<err>.*)