parse pb in python, member is empty if its' value is zero.

[ruinanchen]

In our system, we use golang implement tcp server and python implement a test client. We construct communication protocol base on protocol buffer. I define a pb as follow:

message MsgSendError {
    int64 from_id               = 1;
    int64 to_id                 = 2;
    MsgSendErrorCode error_code = 3;
}
enum MsgSendErrorCode {
    NOT_FRIEND               = 0x00;
    MSG_INVALID              = 0x01;
}

Simple our problem:
Our server construct MsgSendError with error_code's value equal NOT_FRIEND(0x00), then serialize the pb and send binary to client. Our python client parse the binary, but can't extract error_code. If error_code's value equal MSG_INVALID(0x01), error_code could be extracted. Why? Because of python is a dynamic language?

P.S. protoc's version is 3.0.0 in our machine.

[acozzette]

This behavior is actually to be expected, because proto3 does not make a distinction between a primitive field being empty and being set to its default value (which in this case is the 0 value, NOT_FRIEND). In other words, there is no way to distinguish whether error_code was set to NOT_FRIEND or was not set at all. See here for more about proto3 enums: https://developers.google.com/protocol-buffers/docs/proto3#enum

I'll close this issue for now but feel free to reopen it if you have more questions.

[ruinanchen]

Very very thank you. B.T.W, Is there any solution，make python get the default value in this case(even if it actually is empty)? or any suggestion?

[acozzette]

When you access the field you should automatically get the default value (0 or the empty string depending on the type). Could you post some example code if this isn't working?