Knock together a handy py_project macro

tools/build_rules/prelude_bazel

@@ -6,6 +6,7 @@ load("//tools/python:defs.bzl",
      "py_unittest",
      "py_pytest",
      "py_resources",
+     "py_project",
 )
 
 load("@arrdem_source_pypi//:requirements.bzl",

tools/python/defs.bzl

@@ -144,3 +144,37 @@ py_resources = rule(
         ),
     },
 )
+
+def py_project(name=None,
+               lib_srcs=None,
+               lib_deps=None,
+               test_srcs=None,
+               test_deps=None):
+    """
+    A helper for defining conventionally-formatted python project.
+
+    Assumes that there's a src/python tree, and a src/test tree.
+
+    Each test_*.py source generates its own implicit test target. This allows
+    for automatic test parallelism.
+
+    """
+
+    lib_srcs = lib_srcs or native.glob(["src/python/**/*.py"])
+    test_srcs = test_srcs or native.glob(["test/python/**/*.py"])
+
+    py_library(
+        name=name,
+        srcs=lib_srcs,
+        deps=lib_deps,
+        imports=["src/python"],
+    )
+
+    for src in test_srcs:
+        if "test_" in src:
+            py_pytest(
+                name=name + ".test." + str(hash(src)).replace("-", "") + "." + src.split("/")[-1],
+                srcs=test_srcs,
+                deps=[name] + test_deps,
+                imports=["test/python"],
+            )