code: def _default_value_only(self):
          
          line = self.source[self.col_offset:]
          regex = re.compile('''pyconfig\.[eginst]+\(['"][^)]+?['"], ?(.*?)\)''')
          match = regex.match(line)
          if not match:
              return ''
  
          return match.group(1)
docs: Return only the default value, if there is one.