Merge pull request #445 from ecmwf/fix/datetime-conversion

Fix datetime conversion when writing to GRIB. Fixes #444

Author: iainrussell

cfgrib/cfmessage.py

@@ -80,7 +80,7 @@ def to_grib_date_time(
     message, time_ns, date_key="dataDate", time_key="dataTime", epoch=DEFAULT_EPOCH
 ):
     # type: (abc.MutableField, int, str, str, datetime.datetime) -> None
-    time_s = int(time_ns) * 1e-9
+    time_s = time_ns.astype(np.int64) * 1e-9
     time = epoch + datetime.timedelta(seconds=time_s)
     datetime_iso = str(time)
     message[date_key] = int(datetime_iso[:10].replace("-", ""))

tests/test_25_cfmessage.py

@@ -19,7 +19,7 @@ def test_from_grib_date_time() -> None:
 
 def test_to_grib_date_time() -> None:
     message = {}  # type: T.Dict[str, T.Any]
-    datetime_ns = np.datetime64("2001-10-11T01:01:00", "ns").item()
+    datetime_ns = np.datetime64("2001-10-11T01:01:00", "ns")
 
     cfmessage.to_grib_date_time(message, datetime_ns)