Hi pants'ers! Had a quick question about the interplay between the protobuf backend and the mypy plugin. I have a

protobuf_library()

, and in my pants.toml I have

mypy_plugin = true

set for the protobuf backend. When I examine the chroot for

pants typecheck ::

(thanks to

--no-process-execution-local-cleanup

) I see that: • my protobuf_library has accurately generated

.py

and

.pyi

files. • Importantly, I do not see any `__init__.py`s in the protobuf-codegen'd directory. When I run

pants typecheck

, Mypy complains with: "Cannot find implementation or library stub for module named 'your_thing_that_you_imported_pb2'" Interestingly, at runtime (i.e. during a test) this import is resolved correctly. So, at this point, my suspicion is that the codegen is correct and mypy is just not able to find the

.pyi

files. I was browsing through mypy documentation and I came across a seemingly perfect flag:

--namespace-packages

- that accounts for packages lacking init.py. Sure enough, running it with this flag makes it all work swimmingly.

Hey Max, welcome! Sorry for the initial confusion - I have a TODO to better document the interplay of Protobuf and

__init__.py

files. I'm glad you were able to figure this out! FYI the other way you could have resolved this is adding empty

__init__.py

files to the locations where the files get generated to. Usually people don't want to add those to a

src/protos

folder, for example, hence the

python_source_root

option to allow you to have a file like

src/protos/project/models.proto

generate into

src/py/project/models_pb2.py

. Then you would have

src/py/project/__init__.py

and it should work. Does that make sense? Using namespace packages is also totally valid. Although I don't think we want to be activating it by default: we generally try to keep the magic of setting MyPy options to a minimum because it can result in confusion

Yep, that makes sense. I definitely noticed the docs have a lot of warnings of adding init.py - and sure enough, we have stuff in

src/protos

and are not using

python_source_root

.

Ohh I guess I did finish that TODO and never checked it off my list 🙈 https://www.pantsbuild.org/docs/protobuf#step-4-use-the-protobuf_library-in-your-python-code Any feedback on what was confusing there or could be improved? It sounds like a worked out example could help, e.g. linking to Daniel's repo

(slash, it'd be super cool and awesome if you guys could update this repo a bit [it's currently on some weird beta version of pants] and perhaps link it from the "Protobuf and gRPC" page 🙂 )

You would depend on the original `protobuf_library`'s "address", so

src/protos:protos

. Or, use dependency inference which will infer a dep on

my_module_pb2

🙂