rename "Y" freq string to "YE" (pandas parity) (#8629)

* rename "Y" freq string to "YE" (pandas parity) * Update xarray/coding/cftime_offsets.py Co-authored-by: Spencer Clark <spencerkclark@gmail.com> * fix table * changelog * remove unneeded elif branch --------- Co-authored-by: Maximilian Roos <5635139+max-sixty@users.noreply.github.com> Co-authored-by: Spencer Clark <spencerkclark@gmail.com>
pydata · Jan 22, 2024 · 5a92d48 · 5a92d48
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diff --git a/doc/whats-new.rst b/doc/whats-new.rst
@@ -26,10 +26,19 @@ New Features
 Breaking changes
 ~~~~~~~~~~~~~~~~
 
+- Following pandas, :py:meth:`infer_freq` will return ``"YE"``, instead of ``"Y"`` (formerly ``"A"``).
+  This is to be consistent with the deprecation of the latter frequency string in pandas 2.2.
+  This is a follow up to :pull:`8415` (:issue:`8612`, :pull:`8629`).
+  By `Mathias Hauser <https://github.com/mathause>`_.
 
 Deprecations
 ~~~~~~~~~~~~
 
+- Following pandas, the frequency string ``"Y"`` (formerly ``"A"``) is deprecated in
+  favor of ``"YE"``. These strings are used, for example, in :py:func:`date_range`,
+  :py:func:`cftime_range`, :py:meth:`DataArray.resample`, and :py:meth:`Dataset.resample`
+  among others (:issue:`8612`, :pull:`8629`).
+  By `Mathias Hauser <https://github.com/mathause>`_.
 
 Bug fixes
 ~~~~~~~~~

diff --git a/xarray/coding/cftime_offsets.py b/xarray/coding/cftime_offsets.py
@@ -573,7 +573,7 @@ def rollback(self, date):
 
 
 class YearEnd(YearOffset):
-    _freq = "Y"
+    _freq = "YE"
     _day_option = "end"
     _default_month = 12
 
@@ -669,6 +669,7 @@ def _generate_anchored_offsets(base_freq, offset):
     "A": YearEnd,
     "AS": YearBegin,
     "Y": YearEnd,
+    "YE": YearEnd,
     "YS": YearBegin,
     "Q": partial(QuarterEnd, month=12),
     "QE": partial(QuarterEnd, month=12),
@@ -691,6 +692,7 @@ def _generate_anchored_offsets(base_freq, offset):
     **_generate_anchored_offsets("A", YearEnd),
     **_generate_anchored_offsets("YS", YearBegin),
     **_generate_anchored_offsets("Y", YearEnd),
+    **_generate_anchored_offsets("YE", YearEnd),
     **_generate_anchored_offsets("QS", QuarterBegin),
     **_generate_anchored_offsets("Q", QuarterEnd),
     **_generate_anchored_offsets("QE", QuarterEnd),
@@ -716,7 +718,8 @@ def _generate_anchored_deprecated_frequencies(deprecated, recommended):
 
 
 _DEPRECATED_FREQUENICES = {
-    "A": "Y",
+    "A": "YE",
+    "Y": "YE",
     "AS": "YS",
     "Q": "QE",
     "M": "ME",
@@ -725,7 +728,8 @@ def _generate_anchored_deprecated_frequencies(deprecated, recommended):
     "S": "s",
     "L": "ms",
     "U": "us",
-    **_generate_anchored_deprecated_frequencies("A", "Y"),
+    **_generate_anchored_deprecated_frequencies("A", "YE"),
+    **_generate_anchored_deprecated_frequencies("Y", "YE"),
     **_generate_anchored_deprecated_frequencies("AS", "YS"),
     **_generate_anchored_deprecated_frequencies("Q", "QE"),
 }
@@ -979,7 +983,7 @@ def cftime_range(
     +--------+--------------------------+
     | Alias  | Description              |
     +========+==========================+
-    | Y      | Year-end frequency       |
+    | YE     | Year-end frequency       |
     +--------+--------------------------+
     | YS     | Year-start frequency     |
     +--------+--------------------------+
@@ -1009,29 +1013,29 @@ def cftime_range(
     +------------+--------------------------------------------------------------------+
     | Alias      | Description                                                        |
     +============+====================================================================+
-    | Y(S)-JAN   | Annual frequency, anchored at the end (or beginning) of January    |
+    | Y(E,S)-JAN | Annual frequency, anchored at the (end, beginning) of January      |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-FEB   | Annual frequency, anchored at the end (or beginning) of February   |
+    | Y(E,S)-FEB | Annual frequency, anchored at the (end, beginning) of February     |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-MAR   | Annual frequency, anchored at the end (or beginning) of March      |
+    | Y(E,S)-MAR | Annual frequency, anchored at the (end, beginning) of March        |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-APR   | Annual frequency, anchored at the end (or beginning) of April      |
+    | Y(E,S)-APR | Annual frequency, anchored at the (end, beginning) of April        |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-MAY   | Annual frequency, anchored at the end (or beginning) of May        |
+    | Y(E,S)-MAY | Annual frequency, anchored at the (end, beginning) of May          |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-JUN   | Annual frequency, anchored at the end (or beginning) of June       |
+    | Y(E,S)-JUN | Annual frequency, anchored at the (end, beginning) of June         |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-JUL   | Annual frequency, anchored at the end (or beginning) of July       |
+    | Y(E,S)-JUL | Annual frequency, anchored at the (end, beginning) of July         |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-AUG   | Annual frequency, anchored at the end (or beginning) of August     |
+    | Y(E,S)-AUG | Annual frequency, anchored at the (end, beginning) of August       |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-SEP   | Annual frequency, anchored at the end (or beginning) of September  |
+    | Y(E,S)-SEP | Annual frequency, anchored at the (end, beginning) of September    |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-OCT   | Annual frequency, anchored at the end (or beginning) of October    |
+    | Y(E,S)-OCT | Annual frequency, anchored at the (end, beginning) of October      |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-NOV   | Annual frequency, anchored at the end (or beginning) of November   |
+    | Y(E,S)-NOV | Annual frequency, anchored at the (end, beginning) of November     |
     +------------+--------------------------------------------------------------------+
-    | Y(S)-DEC   | Annual frequency, anchored at the end (or beginning) of December   |
+    | Y(E,S)-DEC | Annual frequency, anchored at the (end, beginning) of December     |
     +------------+--------------------------------------------------------------------+
     | Q(E,S)-JAN | Quarter frequency, anchored at the (end, beginning) of January     |
     +------------+--------------------------------------------------------------------+
@@ -1311,11 +1315,8 @@ def date_range_like(source, calendar, use_cftime=None):
             freq = freq.replace("QE", "Q")
         elif isinstance(freq_as_offset, YearBegin) and "YS" in freq:
             freq = freq.replace("YS", "AS")
-        elif isinstance(freq_as_offset, YearEnd) and "Y-" in freq:
-            # Check for and replace "Y-" instead of just "Y" to prevent
-            # corrupting anchored offsets that contain "Y" in the month
-            # abbreviation, e.g. "Y-MAY" -> "A-MAY".
-            freq = freq.replace("Y-", "A-")
+        elif isinstance(freq_as_offset, YearEnd) and "YE" in freq:
+            freq = freq.replace("YE", "A")
 
     use_cftime = _should_cftime_be_used(source, calendar, use_cftime)
 

diff --git a/xarray/tests/test_cftime_offsets.py b/xarray/tests/test_cftime_offsets.py
@@ -157,7 +157,7 @@ def test_year_offset_constructor_invalid_month(offset, invalid_month, exception)
         (MonthBegin(), "MS"),
         (MonthEnd(), "ME"),
         (YearBegin(), "YS-JAN"),
-        (YearEnd(), "Y-DEC"),
+        (YearEnd(), "YE-DEC"),
         (QuarterBegin(), "QS-MAR"),
         (QuarterEnd(), "QE-MAR"),
         (Day(), "D"),
@@ -1387,7 +1387,7 @@ def test_date_range_errors() -> None:
         ("2020-02-01", "ME", "noleap", "gregorian", True, "2020-02-29", True),
         ("2020-02-01", "QE-DEC", "noleap", "gregorian", True, "2020-03-31", True),
         ("2020-02-01", "YS-FEB", "noleap", "gregorian", True, "2020-02-01", True),
-        ("2020-02-01", "Y-FEB", "noleap", "gregorian", True, "2020-02-29", True),
+        ("2020-02-01", "YE-FEB", "noleap", "gregorian", True, "2020-02-29", True),
         ("2020-02-28", "3h", "all_leap", "gregorian", False, "2020-02-28", True),
         ("2020-03-30", "ME", "360_day", "gregorian", False, "2020-03-31", True),
         ("2020-03-31", "ME", "gregorian", "360_day", None, "2020-03-30", False),
@@ -1409,8 +1409,8 @@ def test_date_range_like(start, freq, cal_src, cal_tgt, use_cftime, exp0, exp_pd
         elif "YS" in freq:
             freq = freq.replace("YS", "AS")
             expected_pandas_freq = freq
-        elif "Y-" in freq:
-            freq = freq.replace("Y-", "A-")
+        elif "YE-" in freq:
+            freq = freq.replace("YE-", "A-")
             expected_pandas_freq = freq
         elif "h" in freq:
             expected_pandas_freq = freq.replace("h", "H")
@@ -1534,7 +1534,9 @@ def test_cftime_or_date_range_inclusive_None(function) -> None:
     np.testing.assert_equal(result_None.values, result_both.values)
 
 
-@pytest.mark.parametrize("freq", ["A", "AS", "Q", "M", "H", "T", "S", "L", "U"])
+@pytest.mark.parametrize(
+    "freq", ["A", "AS", "Q", "M", "H", "T", "S", "L", "U", "Y", "A-MAY"]
+)
 def test_to_offset_deprecation_warning(freq):
     # Test for deprecations outlined in GitHub issue #8394
     with pytest.warns(FutureWarning, match="is deprecated"):