def register_backend(format, backend, description=None):
 if (description is None):
  description = u''
 _default_backends[format] = backend
 _default_filetypes[format] = description

def register_backend ( format , backend , description = None ) : if ( description is None ) : description = u'' _default_backends [ format ] = backend _default_filetypes [ format ] = description
register a backend for saving to a given file format .