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Improve warning message and tests for timedelta decoding #10508

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24 changes: 12 additions & 12 deletions xarray/coding/times.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1517,20 +1517,20 @@ def decode(self, variable: Variable, name: T_Name = None) -> Variable:
time_unit = self.time_unit
else:
if self._emit_decode_timedelta_future_warning:
var_string = f"the variable {name!r}" if name else ""
emit_user_level_warning(
"In a future version, xarray will not decode "
"timedelta values based on the presence of a "
"timedelta-like units attribute by default. Instead "
"it will rely on the presence of a timedelta64 dtype "
"attribute, which is now xarray's default way of "
"encoding timedelta64 values. To continue decoding "
"timedeltas based on the presence of a timedelta-like "
"units attribute, users will need to explicitly "
"opt-in by passing True or "
"CFTimedeltaCoder(decode_via_units=True) to "
"decode_timedelta. To silence this warning, set "
"decode_timedelta to True, False, or a "
"'CFTimedeltaCoder' instance.",
f"{var_string} into a timedelta64 dtype based on the "
"presence of a timedelta-like 'units' attribute by "
"default. Instead it will rely on the presence of a "
"timedelta64 'dtype' attribute, which is now xarray's "
"default way of encoding timedelta64 values.\n"
"To continue decoding into a timedelta64 dtype, either "
"set `decode_timedelta=True` when opening this "
"dataset, or add the attribute "
"`dtype='timedelta64[ns]'` to this variable on disk.\n"
"To opt-in to future behavior, set "
"`decode_timedelta=False`.",
FutureWarning,
)
if self.time_unit is None:
Expand Down
30 changes: 22 additions & 8 deletions xarray/tests/test_coding_times.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1867,7 +1867,10 @@ def test_decode_timedelta_via_units(
var = Variable(["time"], timedeltas, encoding=attrs)
encoded = Variable(["time"], np.array([0, 1, 2]), attrs=attrs)
if warns:
with pytest.warns(FutureWarning, match="decode_timedelta"):
with pytest.warns(
FutureWarning,
match="xarray will not decode the variable 'foo' into a timedelta64 dtype",
):
decoded = conventions.decode_cf_variable(
"foo",
encoded,
Expand All @@ -1886,45 +1889,56 @@ def test_decode_timedelta_via_units(


_DECODE_TIMEDELTA_VIA_DTYPE_TESTS = {
"default": (True, None, np.dtype("timedelta64[ns]")),
"decode_timedelta=False": (True, False, np.dtype("int64")),
"decode_timedelta=True": (True, True, np.dtype("timedelta64[ns]")),
"default": (True, None, "ns", np.dtype("timedelta64[ns]")),
"decode_timedelta=False": (True, False, "ns", np.dtype("int64")),
"decode_timedelta=True": (True, True, "ns", np.dtype("timedelta64[ns]")),
"use-original-units": (True, True, "s", np.dtype("timedelta64[s]")),
"inherit-time_unit-from-decode_times": (
CFDatetimeCoder(time_unit="s"),
None,
"ns",
np.dtype("timedelta64[s]"),
),
"set-time_unit-via-CFTimedeltaCoder-decode_times=True": (
True,
CFTimedeltaCoder(time_unit="s"),
"ns",
np.dtype("timedelta64[s]"),
),
"set-time_unit-via-CFTimedeltaCoder-decode_times=False": (
False,
CFTimedeltaCoder(time_unit="s"),
"ns",
np.dtype("timedelta64[s]"),
),
"override-time_unit-from-decode_times": (
CFDatetimeCoder(time_unit="ns"),
CFTimedeltaCoder(time_unit="s"),
"ns",
np.dtype("timedelta64[s]"),
),
"decode-different-units": (
True,
CFTimedeltaCoder(time_unit="us"),
"s",
np.dtype("timedelta64[us]"),
),
}


@pytest.mark.parametrize(
("decode_times", "decode_timedelta", "expected_dtype"),
("decode_times", "decode_timedelta", "original_unit", "expected_dtype"),
list(_DECODE_TIMEDELTA_VIA_DTYPE_TESTS.values()),
ids=list(_DECODE_TIMEDELTA_VIA_DTYPE_TESTS.keys()),
)
def test_decode_timedelta_via_dtype(
decode_times, decode_timedelta, expected_dtype
decode_times, decode_timedelta, original_unit, expected_dtype
) -> None:
timedeltas = pd.timedelta_range(0, freq="D", periods=3)
timedeltas = pd.timedelta_range(0, freq="D", periods=3, unit=original_unit)
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I do not fully understand why mypy complains here, but we have worked around it this way in the past:

Suggested change
timedeltas = pd.timedelta_range(0, freq="D", periods=3, unit=original_unit)
timedeltas = pd.timedelta_range(0, freq="D", periods=3, unit=original_unit) # type: ignore[call-arg]

encoding = {"units": "days"}
var = Variable(["time"], timedeltas, encoding=encoding)
encoded = conventions.encode_cf_variable(var)
assert encoded.attrs["dtype"] == "timedelta64[ns]"
assert encoded.attrs["dtype"] == f"timedelta64[{original_unit}]"
assert encoded.attrs["units"] == encoding["units"]
decoded = conventions.decode_cf_variable(
"foo", encoded, decode_times=decode_times, decode_timedelta=decode_timedelta
Expand Down
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