Bazel should put external repos after stdlib on PYTHONPATH

[rickeylev]

Description of the problem / feature request:

Bazel prepends external dependencies to PYTHONPATH before the stdlib.
This makes external dep modules hide stdlib modules, which is generally a bad thing.

As an example, consider trying to use the enum module with code that is Python 2 and Python 3 compatible. The enum34 package provides the enum module in py2. However, its only a subset of later Python 3 enum features; i.e., its not a drop-in replacement for enum in Python 3.4+

So you create a new_http_archive rule and get the "enum" directory onto sys.path, which now looks something like:
['/some-bazel-path/enum34_archive', 'python3.6/stdlib.zip", "python3.6/site-packages']

Now if you import enum, it'll take the enum module from the enum34_archive entry, which breaks all sorts of things.

Instead, it should really be putting the repos after the stdlib, probably where site-packages would normally go.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

The simplest way is to run a Python 3 binary that depends on the enum34 package.

# WORKSPACE
new_http_archive(
    name = "enum34_archive",
    urls = [
"https://pypi.python.org/packages/bf/3e/31d502c25302814a7c2f1d3959d2a3b3f78e509002ba91aea64993936876/enum34-1.1.6.tar.gz"
        ],
    sha256 = "8ad8c4783bf61ded74527bffb48ed9b54166685e4230386a9ed9b1279e2df5b1",
    strip_prefix="enum34-1.1.6",
    build_file = "enum34.BUILD"
)

# enum34.BUILD:
py_library(
    name = "enum",
    srcs = ["enum/__init__.py"],
    srcs_version = "PY2AND3",
    visibility = ["//visibility:public"],
)

py_binary(
  name = "foo"
  srcs = ["foo.py"]
  deps = ["@enum_archive//:enum"]
)

Then import various stdlib modules in foo.py.

Then run bazel with python3 (I was using 3.6)

bazel build --python_path=/usr/bin/python3.6 :foo
bazel-bin/foo

And it should fail out in some stdlib modules that rely on enum

What operating system are you running Bazel on?

Linux

What's the output of bazel info release?

release 0.16.1

Have you found anything relevant by searching the web?

#2867, while not about this bug, includes some PYTHONPATH output that shows that bazel is putting paths before the stdlib.

[dslomov]

@brandjon

[brandjon]

See #7959 for related sys.path issues.

[github-actions]

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[github-actions]

This issue has been automatically closed due to inactivity. If you're still interested in pursuing this, please reach out to the triage team (@bazelbuild/triage). Thanks!