code: def open(filename, flag="c", protocol=None, writeback=False):
      """Open a persistent dictionary for reading and writing.
  
      The filename parameter is the base filename for the underlying
      database.  As a side-effect, an extension may be added to the
      filename and more than one file may be created.  The optional flag
      parameter has the same interpretation as the flag parameter of
      dbm.open(). The optional protocol parameter specifies the
      version of the pickle protocol.
  
      See the module's __doc__ string for an overview of the interface.
      """
  
      return DbfilenameShelf(filename, flag, protocol, writeback)
  
imports: from pickle import DEFAULT_PROTOCOL, Pickler, Unpickler
  from io import BytesIO
  import collections.abc
label_desc: Use image node_id 1 for calling a global function with example usage: open(filename, flag, protocol, writeback) and returns: DbfilenameShelf