ah, now the CI failure is because it's running python 2 and one of the requirements varies with python version

Collecting funcsigs>=1; python_version < "3.3" (from mock==2.0.0->-r /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/external/rules_python/python/requirements.txt (line 7))
--
  | (In --require-hashes mode, all requirements must have their versions pinned with ==. These do not:
  | funcsigs>=1; python_version < "3.3" from

Hey, I tried to be sneaky and try this out. Did I do it wrong?

1. Update rules_python to this commit, use it in //python (where my requirements.txt is).

diff --git a/WORKSPACE b/WORKSPACE
index 06724b178..15306f4af 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -23,10 +23,10 @@ register_toolchains("//python/interpreter:bfe_py_toolchain")
 ### Load rules_python first so our version wins.
 http_archive(
     name = "rules_python",
-    sha256 = "95ee649313caeb410b438b230f632222fb5d2053e801fe4ae0572eb1d71e95b8",
-    strip_prefix = "rules_python-c8c79aae9aa1b61d199ad03d5fe06338febd0774",
+    sha256 = "72800a67f1aa25d13dfeb8269e1d92c2dfb044792893605238db90b6a0c39a3c",
+    strip_prefix = "rules_python-7175da78d6d032094ea69ab418bc7f8e6f15573a",
     # equivalent SHA to that of 0.1.0 release, except the archive has experimental stuff like wheel.bzl
-    url = "https://github.com/bazelbuild/rules_python/archive/c8c79aae9aa1b61d199ad03d5fe06338febd0774.tar.gz",
+    url = "https://github.com/bazelbuild/rules_python/archive/7175da78d6d032094ea69ab418bc7f8e6f15573a.tar.gz",
 )
 
 load("@rules_python//python:repositories.bzl", "py_repositories")
diff --git a/python/BUILD b/python/BUILD
index ffd0fb0cd..020ee0cc5 100644
--- a/python/BUILD
+++ b/python/BUILD
@@ -1 +1,3 @@
 package(default_visibility = ["//visibility:public"])
+load("@rules_python//python/pip_install:requirements.bzl", "compile_pip_requirements")
+compile_pip_requirements()

2. Then I went into //python and copied requirements.txt to requirements.in.

3. bazel run :requirements.update in //python.

I got this error:

INFO: Invocation ID: 400b5a31-5f0b-487b-8bc5-275ae4a61b1f
DEBUG: /private/var/tmp/_bazel_dhalperin/95eb8687a0f56fe58f756c786043f2ca/external/rules_python/python/repositories.bzl:8:10: py_repositories is a no-op and is deprecated. You can remove this from your WORKSPACE file
DEBUG: /private/var/tmp/_bazel_dhalperin/95eb8687a0f56fe58f756c786043f2ca/external/rules_python/python/legacy_pip_import/pip.bzl:143:10: DEPRECATED: the pip_import rule has been replaced with pip_install, please see rules_python 0.1 release notes
INFO: Analyzed target //python:requirements.update (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //python:requirements.update up-to-date:
  bazel-bin/python/requirements.update
INFO: Elapsed time: 0.307s, Critical Path: 0.02s
INFO: 0 processes.
INFO: Build completed successfully, 1 total action
INFO: Running command line: bazel-bin/python/requirements.update python/requirements.in python/requirements.txt requireINFO: Build completed successfully, 1 total action
Traceback (most recent call last):
  File "/private/var/tmp/_bazel_dhalperin/95eb8687a0f56fe58f756c786043f2ca/execroot/batfish_enterprise/bazel-out/darwin-fastbuild/bin/python/requirements.update.runfiles/rules_python/python/pip_install/pip_compile.py", line 7, in <module>
    from piptools.scripts.compile import cli
  File "/private/var/tmp/_bazel_dhalperin/95eb8687a0f56fe58f756c786043f2ca/execroot/batfish_enterprise/bazel-out/darwin-fastbuild/bin/python/requirements.update.runfiles/pypi__pip_tools/piptools/scripts/compile.py", line 17, in <module>
    from .._compat import parse_requirements
  File "/private/var/tmp/_bazel_dhalperin/95eb8687a0f56fe58f756c786043f2ca/execroot/batfish_enterprise/bazel-out/darwin-fastbuild/bin/python/requirements.update.runfiles/pypi__pip_tools/piptools/_compat/__init__.py", line 5, in <module>
    import six
ModuleNotFoundError: No module named 'six'

FWIW, we are using a custom python interpreter (3.7.9) and our python runtime has no python2 allowed.

Also, sorry for jumping in randomly... don't want to distract too badly from the point of the PR, but if this is a bug (missing dep?) it might be helpful.

I've now test-driven this myself and run into the same error as @dhalperi. As yet I haven't investigated the issue deeply, but I can create the same import problem in my workspace's Nix shell with PYTHONPATH="" python3. six is not stdlib, so I think this is just a dependency of pip_tools that is undeclared in the PR.

Unrelated, but I it was a bit finicky figuring out whether to create the requirements.txt file when setting this up (as an empty file), or let the tool do it. Eg.

bazel build //tools/build/python/...         
INFO: Analyzed 2 targets (0 packages loaded, 0 targets configured).
INFO: Found 2 targets...
ERROR: /Users/jonathon/Code/thundergolfer/foo/tools/build/python/BUILD:3:25: //tools/build/python:requirements.update: missing input file '//tools/build/python:requirements.txt'
ERROR: /Users/jonathon/Code/thundergolfer/foo/tools/build/python/BUILD:3:25 1 input file(s) do not exist
INFO: Elapsed time: 0.115s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
FAILED: Build did NOT complete successfully

So at some point bootstrap instructions would be good to tell users how to smoothly onboard into this.