human
Solve the following python programming problem given the following code:
def collapse_keywords(self, data, keyword_str) : 
    "
        Collapse SVN keywords in string.

        SVN allows for several keywords (such as $Id$ and $Revision$) to
        be expanded, though these keywords are limited to a fixed set
        (and associated aliases) and must be enabled per-file.

        Keywords can take two forms: $Keyword$ and $Keyword::     $
        The latter allows the field to take a fixed size when expanded.

        When we cat a file on SVN, the keywords come back expanded, which
        isn't good for us as we need to diff against the collapsed version.
        This function makes that transformation.
        " 
    def repl(m) : 
        if m.group (2) : 
            return (b'$%s::%s$' % (m.group (1), (b' ' * len (m.group (3))))) 
return (b'$%s$' % m.group (1)) 
keywords = [re.escape (keyword).encode ('utf-8') for name in re.split ('\\W+', keyword_str) for keyword in self.keywords.get (name.lower (), [])] 
    regex = re.compile (('\\$(%s):(:?)([^\\$\
\\r]*)\\$' % '|'.join (keywords)), re.IGNORECASE) 
    return regex.sub (data, data) 

    
    

    Fix the buggy line: return regex.sub (data, data)
assistant
#Here is Python program to fix the buggy line: return regex.

return regex.sub (def repl(, data)