From efa35768b386797a0df4a69b358961df86989736 Mon Sep 17 00:00:00 2001
From: Natalia Mokeeva <natalia.mokeeva.de@gmail.com>
Date: Sat, 8 Nov 2025 22:47:08 +0100
Subject: [PATCH] enh: clarify error message the new usage of the removed year
 frequencies in error message

---
 pandas/_libs/tslibs/offsets.pyx               | 26 +++++++++++++++++++
 .../indexes/datetimes/test_date_range.py      | 16 ++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/pandas/_libs/tslibs/offsets.pyx b/pandas/_libs/tslibs/offsets.pyx
index 66427a0e38847..6f9a1ba34bde9 100644
--- a/pandas/_libs/tslibs/offsets.pyx
+++ b/pandas/_libs/tslibs/offsets.pyx
@@ -5202,6 +5202,32 @@ deprec_to_valid_alias = {
     "L": "ms",
     "U": "us",
     "N": "ns",
+    "AS": "YS",
+    "AS-JAN": "YS-JAN",
+    "AS-FEB": "YS-FEB",
+    "AS-MAR": "YS-MAR",
+    "AS-APR": "YS-APR",
+    "AS-MAY": "YS-MAY",
+    "AS-JUN": "YS-JUN",
+    "AS-JUL": "YS-JUL",
+    "AS-AUG": "YS-AUG",
+    "AS-SEP": "YS-SEP",
+    "AS-OCT": "YS-OCT",
+    "AS-NOV": "YS-NOV",
+    "AS-DEC": "YS-DEC",
+    "A": "Y",
+    "A-JAN": "Y-JAN",
+    "A-FEB": "Y-FEB",
+    "A-MAR": "Y-MAR",
+    "A-APR": "Y-APR",
+    "A-MAY": "Y-MAY",
+    "A-JUN": "Y-JUN",
+    "A-JUL": "Y-JUL",
+    "A-AUG": "Y-AUG",
+    "A-SEP": "Y-SEP",
+    "A-OCT": "Y-OCT",
+    "A-NOV": "Y-NOV",
+    "A-DEC": "Y-DEC",
 }
 
 
diff --git a/pandas/tests/indexes/datetimes/test_date_range.py b/pandas/tests/indexes/datetimes/test_date_range.py
index b179f1b272fac..bb701adaf4c4f 100644
--- a/pandas/tests/indexes/datetimes/test_date_range.py
+++ b/pandas/tests/indexes/datetimes/test_date_range.py
@@ -814,6 +814,22 @@ def test_date_range_depr_lowercase_frequency(self, freq, freq_depr):
             result = date_range("1/1/2000", periods=4, freq=freq_depr)
         tm.assert_index_equal(result, expected)
 
+    @pytest.mark.parametrize(
+        "freq_removed,freq",
+        [
+            ("100A", "Y"),
+            ("2A-DEC", "Y-DEC"),
+            ("100AS", "YS"),
+            ("2AS-MAY", "YS-MAY"),
+        ],
+    )
+    def test_error_message_for_removed_year_yearbegin_frequencies(
+        self, freq, freq_removed
+    ):
+        msg = f"Did you mean {freq}"
+        with pytest.raises(ValueError, match=msg):
+            date_range("1/1/2000", periods=2, freq=freq_removed)
+
 
 class TestDateRangeTZ:
     """Tests for date_range with timezones"""