re.sub replace with matched content
Simply use \1 instead of $1: In [1]: import re In [2]: method = ‘images/:id/huge’ In [3]: re.sub(r'(:[a-z]+)’, r'<span>\1</span>’, method) Out[3]: ‘images/<span>:id</span>/huge’ Also note the use of raw strings (r’…’) for regular expressions. It is not mandatory but removes the need to escape backslashes, arguably making the code slightly more readable.