code: def _IsPresent(item):
    
  
    if item[0].label == _FieldDescriptor.LABEL_REPEATED:
      return bool(item[1])
    elif item[0].cpp_type == _FieldDescriptor.CPPTYPE_MESSAGE:
      return item[1]._is_present_in_parent
    else:
      return True
docs: Given a (FieldDescriptor, value) tuple from _fields, return true if the
    value should be included in the list returned by ListFields().