New JSON renderer that handles datetime objects

Based on the default json serializer from pyramid but it formats datetime
objects as isoformat().

It special cases datetimes without datetime information and assumes they
are in UTC.

This commit introduces this seralizer as a new one on top of the default
`json` as `json_iso_utc` an starts using it on the assignments API.

Short term we'll use this serializer in all dashboard related routes and
longer term we'll replace all uses of json by this seralizer and then will
make it the default.

lms/app.py

@@ -3,6 +3,7 @@
 from sqlalchemy.exc import IntegrityError
 
 from lms.config import configure
+from lms.renderers import json_iso_utc
 
 
 def configure_jinja2_assets(config):
@@ -35,6 +36,9 @@ def create_app(global_config, **settings):  # noqa: ARG001
     config.include("pyramid_jinja2")
     config.include("pyramid_services")
 
+    # Add our own json renderer that handles datetime objects.
+    config.add_renderer("json_iso_utc", json_iso_utc())
+
     # Use pyramid_tm's explicit transaction manager.
     #
     # This means that trying to access a request's transaction after pyramid_tm

lms/renderers.py

@@ -0,0 +1,23 @@
+from datetime import UTC, datetime
+
+from pyramid.renderers import JSON
+
+
+def json_iso_utc():
+    """Return a JSON renderer that formats dates as `isoformat`.
+
+    This renderer assumes datetimes without tz info are in UTC and
+    includes that in the datetime objects so the resulting string
+    includes tz information.
+    """
+
+    renderer = JSON()
+
+    def _datetime_adapter(obj: datetime, _request) -> str:
+        if not obj.tzinfo:
+            obj = obj.replace(tzinfo=UTC)
+        return obj.isoformat()
+
+    renderer.add_adapter(datetime, _datetime_adapter)
+
+    return renderer

lms/views/dashboard/api/assignment.py

@@ -59,7 +59,7 @@ def __init__(self, request) -> None:
     @view_config(
         route_name="api.dashboard.assignments",
         request_method="GET",
-        renderer="json",
+        renderer="json_iso_utc",
         permission=Permissions.DASHBOARD_VIEW,
         schema=ListAssignmentsSchema,
     )
@@ -85,7 +85,7 @@ def assignments(self) -> APIAssignments:
                 APIAssignment(
                     id=assignment.id,
                     title=assignment.title,
-                    created=assignment.created.isoformat(),
+                    created=assignment.created,
                 )
                 for assignment in assignments
             ],
@@ -95,15 +95,15 @@ def assignments(self) -> APIAssignments:
     @view_config(
         route_name="api.dashboard.assignment",
         request_method="GET",
-        renderer="json",
+        renderer="json_iso_utc",
         permission=Permissions.DASHBOARD_VIEW,
     )
     def assignment(self) -> APIAssignment:
         assignment = self.dashboard_service.get_request_assignment(self.request)
         api_assignment = APIAssignment(
             id=assignment.id,
             title=assignment.title,
-            created=assignment.created.isoformat(),
+            created=assignment.created,
             course=APICourse(
                 id=assignment.course.id,
                 title=assignment.course.lms_name,
@@ -128,7 +128,7 @@ def assignment(self) -> APIAssignment:
     @view_config(
         route_name="api.dashboard.course.assignments.metrics",
         request_method="GET",
-        renderer="json",
+        renderer="json_iso_utc",
         permission=Permissions.DASHBOARD_VIEW,
         schema=AssignmentsMetricsSchema,
     )
@@ -191,7 +191,7 @@ def course_assignments_metrics(self) -> APIAssignments:
                 APIAssignment(
                     id=assignment.id,
                     title=assignment.title,
-                    created=assignment.created.isoformat(),
+                    created=assignment.created,
                     course=api_course,
                     annotation_metrics=metrics,
                 )

tests/unit/lms/renderers_test.py

@@ -0,0 +1,28 @@
+from datetime import UTC, datetime
+from unittest.mock import sentinel
+from zoneinfo import ZoneInfo
+
+import pytest
+
+from lms.renderers import json_iso_utc
+
+
+@pytest.mark.parametrize(
+    "time,expected",
+    [
+        # No timezone, UTC is assumed
+        (datetime(2024, 1, 1), "2024-01-01T00:00:00+00:00"),
+        # UTC, UTC is left intact
+        (datetime(2024, 1, 1, tzinfo=UTC), "2024-01-01T00:00:00+00:00"),
+        # Non-UTC, timezone is also left intact
+        (
+            datetime(2024, 1, 1, tzinfo=ZoneInfo("Europe/Madrid")),
+            "2024-01-01T00:00:00+01:00",
+        ),
+    ],
+)
+def test_json_iso_utc(time, expected):
+    assert (
+        json_iso_utc()(sentinel.info)({"time": time}, {})
+        == f"""{{"time": "{expected}"}}"""
+    )

tests/unit/lms/views/dashboard/api/assignment_test.py

@@ -39,7 +39,7 @@ def test_get_assignments(
         )
         assert response == {
             "assignments": [
-                {"id": a.id, "title": a.title, "created": a.created.isoformat()}
+                {"id": a.id, "title": a.title, "created": a.created}
                 for a in assignments
             ],
             "pagination": sentinel.pagination,
@@ -69,7 +69,7 @@ def test_assignment(
         assert response == {
             "id": assignment.id,
             "title": assignment.title,
-            "created": assignment.created.isoformat(),
+            "created": assignment.created,
             "course": {"id": assignment.course.id, "title": assignment.course.lms_name},
         }
 
@@ -96,7 +96,7 @@ def test_assignment_with_auto_grading(
         assert response == {
             "id": assignment.id,
             "title": assignment.title,
-            "created": assignment.created.isoformat(),
+            "created": assignment.created,
             "course": {"id": assignment.course.id, "title": assignment.course.lms_name},
             "groups": [],
             "auto_grading_config": {
@@ -125,7 +125,7 @@ def test_assignment_with_groups(
         assert response == {
             "id": assignment.id,
             "title": assignment.title,
-            "created": assignment.created.isoformat(),
+            "created": assignment.created,
             "course": {"id": assignment.course.id, "title": assignment.course.lms_name},
             "groups": [
                 {"h_authority_provided_id": g.authority_provided_id, "name": g.lms_name}
@@ -152,7 +152,7 @@ def test_assignment_with_sections(
         assert response == {
             "id": assignment.id,
             "title": assignment.title,
-            "created": assignment.created.isoformat(),
+            "created": assignment.created,
             "course": {"id": assignment.course.id, "title": assignment.course.lms_name},
             "sections": [
                 {"h_authority_provided_id": g.authority_provided_id, "name": g.lms_name}
@@ -210,7 +210,7 @@ def test_course_assignments(
                 {
                     "id": assignment.id,
                     "title": assignment.title,
-                    "created": assignment.created.isoformat(),
+                    "created": assignment.created,
                     "course": {
                         "id": course.id,
                         "title": course.lms_name,
@@ -224,7 +224,7 @@ def test_course_assignments(
                 {
                     "id": assignment_with_no_annos.id,
                     "title": assignment_with_no_annos.title,
-                    "created": assignment_with_no_annos.created.isoformat(),
+                    "created": assignment_with_no_annos.created,
                     "course": {
                         "id": course.id,
                         "title": course.lms_name,