Custom toolchains in py_binary (built with --build_python_zip)

[ahoyaharr]

I have an old requirement that our executable Python zips use a hard-coded system interpreter (and not include a hermetic interpreter in the archive). I used to be able to do this with a py_runtime_pair:

load("@bazel_tools//tools/python:toolchain.bzl", "py_runtime_pair")

py_runtime(
    name = "python3_system_runtime",
    interpreter_path = "/usr/bin/python3",
    python_version = "PY3",
    visibility = ["//visibility:public"],
)

py_runtime_pair(
    name = "python3_system_runtime_pair",
    py2_runtime = None,
    py3_runtime = ":python3_system_runtime",
)

toolchain(
    name = "python3_system_toolchain",
    toolchain = ":python3_system_runtime_pair",
    toolchain_type = "@bazel_tools//tools/python:toolchain_type",
)

Now that py_runtime is deprecated

	File "<...>/bazel_tools/tools/python/toolchain.bzl", line 17, column 9, in py_runtime_pair
		fail("@bazel_tools//toolchain.bzl py_runtime_pair is deprecated. Use version from rules_python")

what is the correct way to set this up on the latest (v.1.3.0) version of Python rules?

[rickeylev]

I think all you have to do here is add load("@rules_python//python:py_runtime.bzl", "py_runtime")

See also our docs on setting up custom toolchains: https://rules-python.readthedocs.io/en/latest/toolchains.html