Shorter syntax for optional field

[hongquan]

In proto3, every fields are optional. But in Python code, to declare field as optional, I have to write long lines of code:

def optional_field(number: int) -> dataclasses.Field:
    return field(number, default=None)

@message
@dataclass
class DeviceToServerMessage:
    parking_report: Optional[DeviceDataRequest] = optional_field(1)
    firmware_update_check: Optional[FirmwareUpdateRequest] = optional_field(2)
    reg_request: Optional[DeviceRegistrationRequest] = optional_field(3)
    auth_request: Optional[DeviceAuthenticationRequest] = optional_field(4)
    # For mesh network
    mesh_src: Optional[str] = optional_field(13)

Not only do I have to wrap type with Optional, but also do I have to pass default=None to field() call.

Do you have any idea to make it shorter and look not duplicate?

[eigenein]

Good point, but I need to think about it a little longer to come up with a good solution.

The point is that Optional[...] and default=... are a bit different things. The former declares a field to be nullable, and the latter declares a default value when no value is provided. I also aimed to keep the standard @dataclass usage unchanged. For example, all of these examples are valid:

@dataclass
class Foo:
    bar: Optional[int] = 42  # nullable but default is not `None`

Foo(bar=None)  # still can be set to `None`
Foo()  # or use default `42`
Foo(bar=1)  # or still provide a different value

And this is not valid:

@dataclass
class Foo:
    bar: Optional[int]

Foo()  # `bar` must be provided

But I understand this is a common case to set optional an field to None upon (de-)serialization, so I need to look at different possibilities to minimise number of bad surprises to users

[hongquan]

Could you pre-define the optional_field in pure_protobuf? I think it can be helpful if you plan to make a "code generator" in the future, to generate Python code from *.proto files.

I'm working in an IoT project. To ease the collaboration with firmware developers, I have to keep a *.proto file. They will use some tool to generate to C code and I handcraft the Python code based on it. It would reduce mistake if there is also a tool to generate Python code (in case the proto changes a lot and I lost track).

[eigenein]

True, I'll add the optional_field thingy. I've also created #64 to keep in mind the code generator, which is a really good suggestion

[eigenein]

Sorry for the slow action, the function is now added

[hongquan]

Thank @eigenein