Do not load comm registry entries at startup

Author: joouha

euporie/core/comm/__init__.py

@@ -1,3 +1 @@
 """Sub-module for handling kernel Comm messages."""
-
-from . import ipympl as ipympl

euporie/core/comm/ipywidgets.py

@@ -1457,7 +1457,10 @@ def open_comm_ipywidgets(
         The initialized widget Comm object.
     """
     model_name = data.get("state", {}).get("_model_name")
-    # Skip type checking due to https://github.com/python/mypy/issues/3115
     return WIDGET_MODELS.get(model_name, UnimplementedModel)(
         comm_container, comm_id, data, buffers
-    )  # type: ignore
+    )
+
+
+# Load ``ipympl`` widget
+from . import ipympl as ipympl  # noqa: E402

euporie/core/comm/registry.py

@@ -2,19 +2,19 @@
 
 from __future__ import annotations
 
+from pkgutil import resolve_name
 from typing import TYPE_CHECKING
 
 from euporie.core.comm.base import UnimplementedComm
-from euporie.core.comm.ipywidgets import open_comm_ipywidgets
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
     from typing import Any, Callable
 
     from euporie.core.comm.base import Comm, KernelTab
 
-TARGET_CLASSES: dict[str, Callable[[KernelTab, str, dict, Sequence[bytes]], Comm]] = {
-    "jupyter.widget": open_comm_ipywidgets
+TARGET_CLASSES: dict[str, str] = {
+    "jupyter.widget": "euporie.core.comm.ipywidgets:open_comm_ipywidgets"
 }
 
 
@@ -38,7 +38,13 @@ def open_comm(
 
     """
     target_name = content.get("target_name", "")
-    return TARGET_CLASSES.get(target_name, UnimplementedComm)(
+    if path := TARGET_CLASSES.get(target_name):
+        TargetClass: Callable[[KernelTab, str, dict, Sequence[bytes]], Comm] = (
+            resolve_name(path)
+        )
+    else:
+        TargetClass = UnimplementedComm
+    return TargetClass(
         # comm_container=
         comm_container,
         # comm_id=

tests/test_core_comm_registry.py

@@ -23,13 +23,14 @@ def test_open_comm_ipywidgets() -> None:
     assert isinstance(result, IpyWidgetComm)
 
 
+class TestComm(UnimplementedComm):
+    pass
+
+
 def test_open_comm_with_target_class() -> None:
     """`open_comm` returns an instance of the specified target class."""
 
-    class TestComm(UnimplementedComm):
-        pass
-
-    TARGET_CLASSES["test.target"] = TestComm
+    TARGET_CLASSES["test.target"] = "tests.test_core_comm_registry:TestComm"
     comm_container = Mock(KernelTab)
     content = {
         "target_name": "test.target",