format dates as ISO8601 (#1057)

* format dates as ISO8601

format dates as ISO8601 - currently works for datetimes, but not dates.

Follow up to #18

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update test_jsonutil.py

* Update jsonutil.py

* Update test_jsonutil.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update test_jsonutil.py

* fix date test

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

ipykernel/jsonutil.py

@@ -8,7 +8,7 @@
 import re
 import types
 from binascii import b2a_base64
-from datetime import datetime
+from datetime import date, datetime
 
 from jupyter_client._version import version_info as jupyter_client_version
 
@@ -155,7 +155,7 @@ def json_clean(obj):  # pragma: no cover
         for k, v in obj.items():
             out[str(k)] = json_clean(v)
         return out
-    if isinstance(obj, datetime):
+    if isinstance(obj, datetime) or isinstance(obj, date):
         return obj.strftime(ISO8601)
 
     # we don't understand it, it's probably an unserializable object

ipykernel/tests/test_jsonutil.py

@@ -6,7 +6,7 @@
 import json
 import numbers
 from binascii import a2b_base64
-from datetime import datetime
+from datetime import date, datetime
 
 import pytest
 from jupyter_client._version import version_info as jupyter_client_version
@@ -54,6 +54,7 @@ def test():
         ((x for x in range(3)), [0, 1, 2]),
         (iter([1, 2]), [1, 2]),
         (datetime(1991, 7, 3, 12, 00), "1991-07-03T12:00:00.000000"),
+        (date(1991, 7, 3), "1991-07-03T00:00:00.000000"),
         (MyFloat(), 3.14),
         (MyInt(), 389),
     ]