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Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature (please, look at the "Scope of the project" section in the README.md file)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

#758 reduced the size of artifacts built by the bazel build command with the --build_python_zip option, but there is still room for improvement. The size of the artifacts is at least 43MB (e.g., a zipped python binary which just prints "hello, world"). This is still not great when build artifacts are included to docker images. It turned out that the --build_python_zip option includes the two identical shared libraries (not symlinks), libpython{python_version}.so and libpython{python_version}.so.1.0 into the zip files, but rules_python doesn't use libpython{python_version}.so.
libpython{python_version}.so occupies 16MB (37% of the total size of the artifact of size 43MB). By removing the unused shared library, users of rules_python can deploy smaller Python binaries.

Repro steps

WORKSPACE:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

commit = "9cdb4f3f6aded1ccc62a10d004f9927ccc72702f"

http_archive(
    name = "rules_python",
    sha256 = "7d048c530ca907013565fee907d358314c4cb329622284e07c50be76f2d961ee",
    strip_prefix = "rules_python-" + commit,
    url = "https://github.com/tetsuok/rules_python/archive/" + commit + ".tar.gz",
)

load("@rules_python//python:repositories.bzl", "python_register_toolchains")

python_register_toolchains(
    name = "python3_10",
    python_version = "3.10.4",
)

BUILD:

load("@rules_python//python:defs.bzl", "py_binary")

py_binary(
    name = "hello",
    srcs = ["hello.py"],
)

hello.py:

print("hello, world!")

$ bazel build --build_python_zip //:hello
$ ls -lh bazel-bin/hello.zip
-r-xr-xr-x 1 t docker 43M Jul 29 00:15 bazel-bin/hello.zip

You can see two identical shared libraries, libpython{python_version}.so and libpython{python_version}.so.1.0 into zip files, and the shared libraries dominate the total size of zip files:

$ unzip -l bazel-bin/hello.zip | sort -n | tail -n 6
   745004  2010-01-01 00:00   runfiles/python3_10_x86_64-unknown-linux-gnu/lib/python3.10/pydoc_data/topics.py
   816725  2010-01-01 00:00   runfiles/python3_10_x86_64-unknown-linux-gnu/lib/python3.10/ensurepip/_bundled/setuptools-58.1.0-py3-none-any.whl
  2123599  2010-01-01 00:00   runfiles/python3_10_x86_64-unknown-linux-gnu/lib/python3.10/ensurepip/_bundled/pip-22.0.4-py3-none-any.whl
 38861696  2010-01-01 00:00   runfiles/python3_10_x86_64-unknown-linux-gnu/lib/libpython3.10.so
 38861696  2010-01-01 00:00   runfiles/python3_10_x86_64-unknown-linux-gnu/lib/libpython3.10.so.1.0
110513272                     2381 files

What is the new behavior?

The unused shared library, libpython{python_version}.so included in the hermetic Python toolchain is excluded from Python runfiles built by Python rules. Artifacts built by the bazel build command with the --build_python_zip get smaller. The size of the resulting zipped Python executables reduces by 16 MB (43 MB → 27 MB in the above example).

Does this PR introduce a breaking change?

• Yes
• No

Other information