Understand Protobuf enum in python

In grpc-mate's protobuf definition, we defined some enum types, when we compile them into python code, it may confuse people on how to use it , especially for the enum defined inside protobuf message

standalone enum types

enum ProductStatus {
    InStock = 0;
    OutStock = 1;
}

when compile such enum into python code , it will be like below

_PRODUCTSTATUS = _descriptor.EnumDescriptor(
  name='ProductStatus',
  full_name='ProductStatus',
  filename=None,
  file=DESCRIPTOR,
  values=[
    _descriptor.EnumValueDescriptor(
      name='InStock', index=0, number=0,
      serialized_options=None,
      type=None),
    _descriptor.EnumValueDescriptor(
      name='OutStock', index=1, number=1,
      serialized_options=None,
      type=None),
  ],
  containing_type=None,
  serialized_options=None,
  serialized_start=196,
  serialized_end=238,
)
_sym_db.RegisterEnumDescriptor(_PRODUCTSTATUS)

ProductStatus = enum_type_wrapper.EnumTypeWrapper(_PRODUCTSTATUS)
InStock = 0
OutStock = 1

the enum type will be just a number but with it's Own name, we could import the enum like from grpc_mate.product_common_pb2 import InStock

nested enum type inside protobuf message

message UploadProductResponse {
    enum ResultStatus {
        SUCCESS = 0;
        FAILED = 1;
    }
    ResultStatus result_status = 1;
}

it will be compiled as python code like below

_UPLOADPRODUCTRESPONSE_RESULTSTATUS = _descriptor.EnumDescriptor(
  name='ResultStatus',
  full_name='UploadProductResponse.ResultStatus',
  filename=None,
  file=DESCRIPTOR,
  values=[
    _descriptor.EnumValueDescriptor(
      name='SUCCESS', index=0, number=0,
      serialized_options=None,
      type=None),
    _descriptor.EnumValueDescriptor(
      name='FAILED', index=1, number=1,
      serialized_options=None,
      type=None),
  ],
  containing_type=None,
  serialized_options=None,
  serialized_start=188,
  serialized_end=227,
)
_sym_db.RegisterEnumDescriptor(_UPLOADPRODUCTRESPONSE_RESULTSTATUS)

lots of people will get confused on how to use ResultStatus enum inside UploadProductResponse, due to python's launage features, we could access such enum as UploadProductResponse.SUCCESS or UploadProductResponse.FAILED. as I said in last section, the enum in python is just a number, we could also access the number like UploadProductResponse.ResultStatus.Value('SUCCESS') -> 0, or access it's name via UploadProductResponse.ResultStatus.Name(0) -> 'SUCCESS'. all the methods are defined in enum_type_wrapper.py.