8000 Port negative frequency fix from date_range to cftime_range · pydata/xarray@709ba6c · GitHub
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spencerkclarkspencerkclark
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Port negative frequency fix from date_range to cftime_range
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‎doc/whats-new.rst

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@@ -58,6 +58,12 @@ Breaking changes
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Bug fixes
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~~~~~~~~~
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- Following `an upstream bug fix
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<https://github.com/pandas-dev/pandas/issues/56147>`_ to
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:py:func:`pandas.date_range`, date ranges produced by
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:py:func:`xarray.cftime_range` with negative frequencies will now fall fully
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within the bounds of the provided start and end dates (:pull:`8999`). By
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`Spencer Clark <https://github.com/spencerkclark>`_.
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Internal Changes

‎xarray/coding/cftime_offsets.py

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@@ -845,7 +845,12 @@ def _generate_range(start, end, periods, offset):
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A generator object
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"""
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if start:
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start = offset.rollforward(start)
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# From pandas GH 56147 / 56832 to account for negative direction and
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# range bounds
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if offset.n >= 0:
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start = offset.rollforward(start)
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else:
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start = offset.rollback(start)
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if periods is None and end < start and offset.n >= 0:
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end = None

‎xarray/tests/__init__.py

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@@ -130,6 +130,7 @@ def _importorskip(
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has_numexpr, requires_numexpr = _importorskip("numexpr")
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has_flox, requires_flox = _importorskip("flox")
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has_pandas_ge_2_2, __ = _importorskip("pandas", "2.2")
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has_pandas_3, requires_pandas_3 = _importorskip("pandas", "3.0.0.dev0")
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# some special cases

‎xarray/tests/test_cftime_offsets.py

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@@ -42,6 +42,7 @@
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has_cftime,
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has_pandas_ge_2_2,
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requires_cftime,
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requires_pandas_3,
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)
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cftime = pytest.importorskip("cftime")
@@ -1354,7 +1355,7 @@ def test_calendar_specific_month_end_negative_freq(
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) -> None:
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year = 2000 # Use a leap-year to highlight calendar differences
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result = cftime_range(
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start="2000-12",
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start="2001",
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end="2000",
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freq="-2ME",
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calendar=calendar,
@@ -1464,7 +1465,7 @@ def test_date_range_errors() -> None:
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("2020-02-01", "QE-DEC", "noleap", "gregorian", True, "2020-03-31", True),
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("2020-02-01", "YS-FEB", "noleap", "gregorian", True, "2020-02-01", True),
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("2020-02-01", "YE-FEB", "noleap", "gregorian", True, "2020-02-29", True),
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("2020-02-01", "-1YE-FEB", "noleap", "gregorian", True, "2020-02-29", True),
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("2020-02-01", "-1YE-FEB", "noleap", "gregorian", True, "2019-02-28", True),
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("2020-02-28", "3h", "all_leap", "gregorian", False, "2020-02-28", True),
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("2020-03-30", "ME", "360_day", "gregorian", False, "2020-03-31", True),
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("2020-03-31", "ME", "gregorian", "360_day", None, "2020-03-30", False),
@@ -1724,7 +1725,17 @@ def test_new_to_legacy_freq_pd_freq_passthrough(freq, expected):
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@pytest.mark.parametrize("start", ("2000", "2001"))
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@pytest.mark.parametrize("end", ("2000", "2001"))
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@pytest.mark.parametrize(
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"freq", ("MS", "-1MS", "YS", "-1YS", "ME", "-1ME", "YE", "-1YE")
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"freq",
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(
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"MS",
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pytest.param("-1MS", marks=requires_pandas_3),
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"YS",
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pytest.param("-1YS", marks=requires_pandas_3),
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"ME",
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pytest.param("-1ME", marks=requires_pandas_3),
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"YE",
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pytest.param("-1YE", marks=requires_pandas_3),
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),
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)
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def test_cftime_range_same_as_pandas(start, end, freq):
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result = date_range(start, end, freq=freq, calendar="standard", use_cftime=True)

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