code: def get_placeholders_list(self, format_string, matches=None):
          
          if format_string not in self._format_placeholders:
              placeholders = self._formatter.get_placeholders(format_string)
              self._format_placeholders[format_string] = placeholders
          else:
              placeholders = self._format_placeholders[format_string]
  
          if not matches:
              return list(placeholders)
          elif isinstance(matches, basestring):
              matches = [matches]
          # filter matches
          found = set()
          for match in matches:
              for placeholder in placeholders:
                  if fnmatch(placeholder, match):
                      found.add(placeholder)
          return list(found)
docs: Returns a list of placeholders in ``format_string``.
  
          If ``matches`` is provided then it is used to filter the result
          using fnmatch so the following patterns can be used:
  
  
          .. code-block:: none
  
              * 	    matches everything
              ? 	    matches any single character
              [seq] 	matches any character in seq
              [!seq] 	matches any character not in seq
  
          This is useful because we just get simple placeholder without any
          formatting that may be applied to them
          eg ``'{placeholder:.2f}'`` will give ``['{placeholder}']``