code: def add_default_handler(ioclass, format, extension=None):
      
      if format in _handler_map:
          print("Warning: format {} already present.".format(format))
  
      _handler_map[format] = ioclass
  
      if extension in _extensions_map:
          print("Warning: extension {} already handled by {} handler."
                .format(extension, _extensions_map[extension]))
  
      if extension is not None:
          _extensions_map[extension] = format
docs: Register a new data handler for a given format in
         the default handler list.
  
         This is a convenience function used internally to setup the
         default handlers. It can be used to add other handlers at
         runtime even if this isn't a suggested practice.
  
         **Parameters**
  
         ioclass: IOHandler subclass
         format: str
           A string identifier representing the format
         extension: str, optional
           The file extension associated with the format.