Add Python2 PEX support

Python3 to follow next.

WORKSPACE

@@ -53,3 +53,20 @@ http_archive(
 )
 load("@rules_pkg//:deps.bzl", "rules_pkg_dependencies")
 rules_pkg_dependencies()
+
+http_archive(
+    name = "io_bazel_rules_pex",
+    strip_prefix = "bazel_rules_pex-0.3.0",
+    urls = [
+        "https://github.com/benley/bazel_rules_pex/archive/refs/tags/0.3.0.tar.gz",
+    ],
+    sha256 = "25b203ed474f1e8d4060a00dee1bcefb9ec487c817b868a315ccbe8ca3b08a9f",
+    patch_args = [
+	"-p1",
+    ],
+    patches = [
+	"//third_party:pex.patch",
+    ],
+)
+load("@io_bazel_rules_pex//pex:pex_rules.bzl", "pex_repositories")
+pex_repositories()

python_pdm_example/BUILD

@@ -0,0 +1,12 @@
+load("@io_bazel_rules_pex//pex:pex_rules.bzl", "pex_binary", "pex_library", "pex_test", "pex_pytest")
+
+pex_binary(
+    name = "app",
+    srcs = [
+        "app.py",
+	"__init__.py",
+    ],
+    reqs = [
+	"flask",
+    ],
+)

python_pdm_example/README.md

@@ -22,3 +22,16 @@ fi
 
 When inside the directory, just run `pdm install` and you're ready to run the
 app with `python app.py`.
+
+## Bazel PEX Python2
+
+If you want to build a Python2 pex file, run:
+
+```
+bazel build //python_pdm_example:app --host_force_python=PY2
+```
+
+You can run the resulting file as:
+```
+bazel-bin/python_pdm_example/app
+```