Regular expression: match start or whitespace

Question

Can a regular expression match whitespace or the start of a string?

I\'m trying to replace currency the abbreviation GBP with a £ symbol. I

Answer 1

This replaces GBP if it's preceded by the start of a string or a word boundary (which the start of a string already is), and after GBP comes a numeric value or a word boundary:

re.sub(u'\bGBP(?=\b|\d)', u'£', text)

This removes the need for any unnecessary backreferencing by using a lookahead. Inclusive enough?