diff --git a/tools/platforms/python/BUILD b/tools/platforms/python/BUILD
new file mode 100644
index 0000000..da13bbd
--- /dev/null
+++ b/tools/platforms/python/BUILD
@@ -0,0 +1,21 @@
+# TODO(phil): Delete this file after migrating everything to use upstream pip
+# rules.
+
+package(default_visibility = ["//visibility:public"])
+
+constraint_setting(
+    name = "python_source",
+    default_constraint_value = ":debian_bundled_python",
+)
+
+# Python code taken from .deb packages.
+constraint_value(
+    name = "debian_bundled_python",
+    constraint_setting = ":python_source",
+)
+
+# Python code taken from pypi.org.
+constraint_value(
+    name = "upstream_bundled_python",
+    constraint_setting = ":python_source",
+)