core/compat: move fromisoformat to .core.compat module

my/core/compat.py

@@ -76,3 +76,42 @@ if sys.version_info[:2] <= (3, 9):
         return lo
 else:
     from bisect import bisect_left
+
+
+from datetime import datetime
+if sys.version_info[:2] >= (3, 11):
+    fromisoformat = datetime.fromisoformat
+else:
+    def fromisoformat(date_string: str) -> datetime:
+        # didn't support Z as "utc" before 3.11
+        if date_string.endswith('Z'):
+            # NOTE: can be removed from 3.11?
+            # https://docs.python.org/3/library/datetime.html#datetime.datetime.fromisoformat
+            date_string = date_string[:-1] + '+00:00'
+        return datetime.fromisoformat(date_string)
+
+
+def test_fromisoformat() -> None:
+    from datetime import timezone
+
+    # feedbin has this format
+    assert fromisoformat('2020-05-01T10:32:02.925961Z') == datetime(
+        2020, 5, 1, 10, 32, 2, 925961, timezone.utc,
+    )
+
+    # polar has this format
+    assert fromisoformat('2018-11-28T22:04:01.304Z') == datetime(
+        2018, 11, 28, 22, 4, 1, 304000, timezone.utc,
+    )
+
+    # stackexchange, runnerup has this format
+    assert fromisoformat('2020-11-30T00:53:12Z') == datetime(
+        2020, 11, 30, 0, 53, 12, 0, timezone.utc,
+    )
+
+    # arbtt has this format (sometimes less/more than 6 digits in milliseconds)
+    # TODO doesn't work atm, not sure if really should be supported...
+    # maybe should have flags for weird formats?
+    # assert isoparse('2017-07-18T18:59:38.21731Z') == datetime(
+    #     2017, 7, 18, 18, 59, 38, 217310, timezone.utc,
+    # )