Refactor load_python_class and add _import_module_from_classpath for improved module handling; enhance test cases for classpath conflicts

Author: grongierisc

src/iop/_persistent_message.py

@@ -299,8 +299,10 @@ def load_python_class(
     except ModuleNotFoundError as exc:
         if not python_classpath or not _is_missing_target_module(exc, module_name):
             raise
-        _prepend_sys_path(python_classpath)
-        module = importlib.import_module(module_name)
+        module = _import_module_from_classpath(module_name, python_classpath)
+    else:
+        if python_classpath and not hasattr(module, class_name):
+            module = _import_module_from_classpath(module_name, python_classpath)
     return getattr(module, class_name)
 
 
@@ -529,3 +531,10 @@ def _prepend_sys_path(path: str) -> None:
     while normalized_path in sys.path:
         sys.path.remove(normalized_path)
     sys.path.insert(0, normalized_path)
+    importlib.invalidate_caches()
+
+
+def _import_module_from_classpath(module_name: str, python_classpath: str):
+    _prepend_sys_path(python_classpath)
+    sys.modules.pop(module_name, None)
+    return importlib.import_module(module_name)

src/tests/e2e/local/test_persistent_message.py

@@ -1,4 +1,5 @@
 """E2E (local IRIS) tests for PersistentMessage native message bodies."""
+
 from unittest.mock import MagicMock
 
 from iop import Field, PersistentMessage

src/tests/unit/test_persistent_message.py

@@ -70,10 +70,12 @@ def test_classes_registration_uses_key_as_iris_classname():
 
     assert NativeOrderMessage._classname == "Demo.Msg.NativeOrderMessage"
     assert NativeOrderMessage._parameters["IOP_MESSAGE_KIND"] == "PersistentMessage"
-    assert NativeOrderMessage._parameters["IOP_PYTHON_CLASS"].endswith(".NativeOrderMessage")
-    assert NativeOrderMessage._parameters["IOP_PYTHON_CLASSPATH"] == get_python_classpath(
-        NativeOrderMessage
+    assert NativeOrderMessage._parameters["IOP_PYTHON_CLASS"].endswith(
+        ".NativeOrderMessage"
     )
+    assert NativeOrderMessage._parameters[
+        "IOP_PYTHON_CLASSPATH"
+    ] == get_python_classpath(NativeOrderMessage)
 
 
 def test_explicit_meta_classname_conflict_raises():
@@ -182,18 +184,27 @@ def _Id(self):
 
 def test_load_python_class_uses_classpath_on_cold_import(tmp_path):
     app_dir = tmp_path / "app"
+    conflict_dir = tmp_path / "conflict"
     app_dir.mkdir()
+    conflict_dir.mkdir()
     module_path = app_dir / "msg.py"
     module_path.write_text(
         "from iop import Field, PersistentMessage\n"
         "class ColdMessage(PersistentMessage):\n"
         "    Value: str = Field(required=True)\n",
         encoding="utf-8",
     )
+    (conflict_dir / "msg.py").write_text(
+        "class PickleMessage:\n    pass\n",
+        encoding="utf-8",
+    )
 
     sys.modules.pop("msg", None)
     while str(app_dir) in sys.path:
         sys.path.remove(str(app_dir))
+    while str(conflict_dir) in sys.path:
+        sys.path.remove(str(conflict_dir))
+    sys.path.insert(0, str(conflict_dir))
 
     try:
         msg_cls = load_python_class("msg.ColdMessage", str(app_dir))
@@ -205,6 +216,8 @@ def test_load_python_class_uses_classpath_on_cold_import(tmp_path):
         sys.modules.pop("msg", None)
         while str(app_dir) in sys.path:
             sys.path.remove(str(app_dir))
+        while str(conflict_dir) in sys.path:
+            sys.path.remove(str(conflict_dir))
 
 
 def test_deserializes_iris_originated_message_with_class_parameters(tmp_path):