Support date serialization in messages (#1060)

Author: sebwills

jupyter_client/jsonutil.py

@@ -8,7 +8,7 @@
 import warnings
 from binascii import b2a_base64
 from collections.abc import Iterable
-from datetime import datetime
+from datetime import date, datetime
 from typing import Any, Optional, Union
 
 from dateutil.parser import isoparse as _dateutil_parse
@@ -110,6 +110,9 @@ def json_default(obj: Any) -> Any:
         obj = _ensure_tzinfo(obj)
         return obj.isoformat().replace("+00:00", "Z")
 
+    if isinstance(obj, date):
+        return obj.isoformat()
+
     if isinstance(obj, bytes):
         return b2a_base64(obj, newline=False).decode("ascii")
 
@@ -185,7 +188,7 @@ def json_clean(obj: Any) -> Any:
             out[str(k)] = json_clean(v)
         return out
 
-    if isinstance(obj, datetime):
+    if isinstance(obj, (datetime, date)):
         return obj.strftime(ISO8601)
 
     # we don't understand it, it's probably an unserializable object

tests/test_jsonutil.py

@@ -139,7 +139,7 @@ def test_parse_ms_precision():
             assert isinstance(parsed, str)
 
 
-def test_json_default_date():
+def test_json_default_datetime():
     naive = datetime.datetime.now()  # noqa
     local = tzoffset("Local", -8 * 3600)
     other = tzoffset("Other", 2 * 3600)
@@ -178,6 +178,7 @@ def test_json_default():
         (iter([1, 2]), [1, 2]),
         (MyFloat(), 3.14),
         (MyInt(), 389),
+        (datetime.date(2025, 4, 8), "2025-04-08"),
     ]
 
     for val, jval in pairs: