`bazel run py_binary` loads incorrect module with same name

py_binary can end up importing a file from the source tree that it doesn’t depend on. It can also get confused by stale .pyc files that Python writes into the source tree (is that expected behaviour?), even once this file has been removed.

My example may seem contrived, but I ran into this problem when trying to port the rosmaster script to Python - since Bazel rejects Python files without the .py extension, I renamed it to rosmaster.py. This caused it to import itself and fail. After I renamed it to avoid this, I had to manually delete the .pyc file before bazel run would work.

Repro

> echo > WORKSPACE 
> cat lib/hello.py 
def hello():
  print("hello, world!")
> cat bin/hello2.py 
import hello

if __name__ == "__main__":
  print "loaded hello from", hello.__file__
  hello.hello()
> cp bin/hello2.py bin/hello.py  
> cat BUILD.bazel 
py_library(
    name = "hello_lib",
    srcs = ["lib/hello.py"],
    imports = ["lib"],
)

py_binary(
    name = "hello2",
    srcs = ["bin/hello2.py"],
    deps = [":hello_lib"],
)
> bazel run :hello2
[SNIP: build output]
INFO: Running command line: bazel-bin/hello2
loaded hello from /usr/local/google/home/rodrigoq/git/bazeltest/stale_pyc/bin/hello.py
Traceback (most recent call last):
  File "/usr/local/google/home/rodrigoq/.cache/bazel/_bazel_rodrigoq/64c22e296c4c5490bc13ab2111abf684/execroot/__main__/bazel-out/local-fastbuild/bin/hello2.runfiles/__main__/bin/hello2.py", line 5, in <module>
    hello.hello()
TypeError: 'module' object is not callable
ERROR: Non-zero return code '1' from command: Process exited with status 1
> rm bin/hello.py 
> bazel run :hello2
[SNIP: build output]
INFO: Running command line: bazel-bin/hello2
loaded hello from /usr/local/google/home/rodrigoq/git/bazeltest/stale_pyc/bin/hello.pyc
Traceback (most recent call last):
  File "/usr/local/google/home/rodrigoq/.cache/bazel/_bazel_rodrigoq/64c22e296c4c5490bc13ab2111abf684/execroot/__main__/bazel-out/local-fastbuild/bin/hello2.runfiles/__main__/bin/hello2.py", line 5, in <module>
    hello.hello()
TypeError: 'module' object is not callable
ERROR: Non-zero return code '1' from command: Process exited with status 1
> rm bin/hello.pyc
> bazel run :hello2
[SNIP: build output]
INFO: Running command line: bazel-bin/hello2
loaded hello from /usr/local/google/home/rodrigoq/.cache/bazel/_bazel_rodrigoq/64c22e296c4c5490bc13ab2111abf684/execroot/__main__/bazel-out/local-fastbuild/bin/hello2.runfiles/__main__/lib/hello.pyc
hello, world!

Environment info

• Operating System: Ubuntu 14.04
• Bazel version: 0.7.0

[drigz]

@scottcjt If I’m understanding right, I’ve run into that issue too (Python confusing the external repo with the module directory). We use one of two workarounds:

• for simple modules (with just one file, eg mock), use a genrule to rename mock.py to __init__.py in the repository root, so that Python can find everything in the repo root
• otherwise, make sure the repo name doesn’t match the module name (eg use @flatbuffers_repo//:runtime_py)

Hope that helps…

[keith]

I wonder if this is the same issue as https://github.com/bazelbuild/bazel/issues/7754 ?