code: def format_contains(self, format_string, names):
          
          # We cache things to prevent parsing the format_string more than needed
          if isinstance(names, list):
              key = str(names)
          else:
              key = names
              names = [names]
          try:
              return self._format_placeholders_cache[format_string][key]
          except KeyError:
              pass
  
          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 format_string not in self._format_placeholders_cache:
              self._format_placeholders_cache[format_string] = {}
  
          for name in names:
              for placeholder in placeholders:
                  if fnmatch(placeholder, name):
                      self._format_placeholders_cache[format_string][key] = True
                      return True
          self._format_placeholders_cache[format_string][key] = False
          return False
docs: Determines if ``format_string`` contains a placeholder string ``names``
          or a list of placeholders ``names``.
  
          ``names`` is tested against placeholders 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 a simple test like
          ``'{placeholder}' in format_string``
          will fail if the format string contains placeholder formatting
          eg ``'{placeholder:.2f}'``