bazel-python-proto-import-error

Demonstration of import problem when using Bazel to build python binary where the protos being imported reside in different directories.

Details

My py_binary cannot run due to an import error. The python code relies on a protobuf as dependency. That protobuf in turn depends on another protobuf in a subdirectory. It is this pattern which seems to cause the issue as it only emerges once sub_dependency_proto.proto is introduced.

The error seems to stem from the generated python code for the protobuf where the import statement does not reflect the directory structure that Bazel assembles.

Strangely, the python code works fine as a compiled library and test, indicating something strange is going on with py_binary.

Introducing the flag build --incompatible_default_to_explicit_init_py to .bazelrc solves the problem for running the binary directory, but if the executable is called via a custom rule then the problem persists:

Failing Command (custom rule)

• bazel build //hello_world_printer/src:hello_world_via_custom_rule

Successful Commands (library, test, and direct call to binary)

• bazel run //hello_world_printer/src:hello_world
• bazel build //hello_world_printer/src:hello_world_library
• bazel test //hello_world_printer/src:hello_world_test

Any help would be much appreciated 😕

Error message

File "<REDACTED>/demo_bazel_issue/hello_world_printer/protos/same_directory_proto_python_pb/hello_world_printer/protos/same_directory_proto_pb2.py", line 15, in <module>
from distinct_directory.protos import distinct_directory_proto_pb2 as distinct__directory_dot_protos_dot_distinct__directory__proto__pb2
ImportError: cannot import name 'distinct_directory_proto_pb2' from 'distinct_directory.protos'