Support decoding unsigned integers to timedelta (#10972)

Author: dcherian

doc/whats-new.rst

@@ -46,6 +46,9 @@ Bug Fixes
   By `Justus Magin <https://github.com/keewis>`_.
 - Avoid casting custom indexes in ``Dataset.drop_attrs`` (:pull:`10961`)
   By `Justus Magin <https://github.com/keewis>`_.
+- Support decoding unsigned integers to ``np.timedelta64``.
+  By `Deepak Cherian <https://github.com/dcherian>`_.
+
 
 Documentation
 ~~~~~~~~~~~~~

xarray/coding/times.py

@@ -626,6 +626,8 @@ def _numbers_to_timedelta(
         nan = np.asarray(np.isnan(flat_num))
     elif flat_num.dtype.kind == "i":
         nan = np.asarray(flat_num == np.iinfo(np.int64).min)
+    elif flat_num.dtype.kind == "u":
+        nan = np.broadcast_to(np.asarray(False), flat_num.shape)
 
     # in case we need to change the unit, we fix the numbers here
     # this should be safe, as errors would have been raised above

xarray/tests/test_coding_times.py

@@ -1950,6 +1950,15 @@ def test_decode_timedelta_via_dtype(
     assert decoded.dtype == expected_dtype
 
 
+@pytest.mark.parametrize("dtype", [np.uint64, np.int64, np.float64])
+def test_decode_timedelta_dtypes(dtype) -> None:
+    encoded = Variable(["time"], np.arange(10), {"units": "seconds"})
+    coder = CFTimedeltaCoder(time_unit="s")
+    decoded = coder.decode(encoded)
+    assert decoded.dtype.kind == "m"
+    assert_equal(coder.encode(decoded), encoded)
+
+
 def test_lazy_decode_timedelta_unexpected_dtype() -> None:
     attrs = {"units": "seconds"}
     encoded = Variable(["time"], [0, 0.5, 1], attrs=attrs)