Python equivalent to "include" paths

[glin...@gmail.com]

Since bazel is already setting up a wrapper around python binaries when launching, it would be great to have an equivalent to the C++ include paths. This would make it nicer to work with dependent libraries imported into the source tree.

ie.
/third_party/bar/BUILD - an imported library, wrapped in py_library
/third_party/foo/BUILD - an imported library, wrapped in py_library, depends on bar

I now have to fix up all references to bar inside of foo. ie. "import bar" becomes "import third_party.bar". If there aren't good unit tests in the library, this becomes a fairly error prone process.

Is this possible in the current system?

Thanks!

[Damien Martin-guillerez]

Do you mean to add third_party to the PYTHONPATH?

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[glin...@gmail.com]

On Wednesday, December 2, 2015 at 1:48:21 PM UTC-8, Damien Martin-guillerez wrote:
> Do you mean to add third_party to the PYTHONPATH?
>

Yes, that's possible. Having it happen from the rule (similar to the includes in cc_library) would be nicer, as then I don't have to have some outside setup step. It looks like there is already a fair bit of infrastructure in python binaries around the runfiles -- that's what led me to think there might be some way to do this.

[Austin Schuh]

On Wed, Dec 2, 2015 at 1:58 PM <glin...@gmail.com> wrote:

On Wednesday, December 2, 2015 at 1:48:21 PM UTC-8, Damien Martin-guillerez wrote:
> Do you mean to add third_party to the PYTHONPATH?
>
Yes, that's possible.  Having it happen from the rule (similar to the includes in cc_library) would be nicer, as then I don't have to have some outside setup step.  It looks like there is already a fair bit of infrastructure in python binaries around the runfiles -- that's what led me to think there might be some way to do this.

I've been looking for this as well!  Whenever we use the python protobuf library checked into third_party in our repo, we have to modify PYTHONPATH in each python file that includes it to add it so that things will load.  Having a way to get it added automatically to PYTHONPATH would be amazing.

Austin

[Benjamin Staffin]

I've had some luck with creating a third_party/__init__.py file with the following contents:

import os
import sys
sys.path.append(os.path.join(os.path.dirname(os.path.abspath(__file__)), 'py')
del os
del sys

Then in my code I just "import third_party" before importing any libraries from third_party/py/ and I'm good to go:

#!/usr/bin/env python
import third_party
import thing.inside.third.party

If there's a better way of doing this, I'd love to hear about it.  I really want to have better python support in Bazel in general, and am willing to put some effort into making it happen.

[Brian Silverman]

I agree that having better Bazel support for this would be nice. Maybe something like pkg_tar's strip_prefix?

For now, I was having issues with something similar to that sys.path manipulation preferring .py files from /usr/, plus having to "import third_party" first is annoying. To fix this, I created an external repository with a thing/__init__.py file that looks like this:

import sys

import third_party.thing.inside

sys.modules['thing.inside'] = third_party.thing.inside

Including a py_library with thing/__init__.py in a py_binary works nicely AFAIK ("import thing.inside.third.party" just works and the library importing parts of itself works too).

I went with a new_http_archive using an empty archive and a genrule in the .BUILD file to generate thing/__init__.py to avoid managing versions of something external, but any of the external repository types should work.

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