From cd9a43b4c993a8bef0c0d35e010bdaadeb1e9926 Mon Sep 17 00:00:00 2001
From: Natalia Mokeeva <natalia.mokeeva.de@gmail.com>
Date: Wed, 13 Dec 2023 19:52:04 +0100
Subject: [PATCH 1/2] raise ValueError if invalid period freq pass to asfreq

---
 pandas/core/resample.py                    |  8 +++++++-
 pandas/tests/resample/test_period_index.py | 17 +++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/pandas/core/resample.py b/pandas/core/resample.py
index d54f6d31f6144..8864e7e8db93e 100644
--- a/pandas/core/resample.py
+++ b/pandas/core/resample.py
@@ -2784,7 +2784,13 @@ def asfreq(
             how = "E"
 
         if isinstance(freq, BaseOffset):
-            freq = freq_to_period_freqstr(freq.n, freq.name)
+            if hasattr(freq, "_period_dtype_code"):
+                freq = freq_to_period_freqstr(freq.n, freq.name)
+            else:
+                raise ValueError(
+                    f"Invalid offset: '{freq.base}' for converting time series "
+                    f"with PeriodIndex."
+                )
 
         new_obj = obj.copy()
         new_obj.index = obj.index.asfreq(freq, how=how)
diff --git a/pandas/tests/resample/test_period_index.py b/pandas/tests/resample/test_period_index.py
index 60b222179ba12..9663d35587c6e 100644
--- a/pandas/tests/resample/test_period_index.py
+++ b/pandas/tests/resample/test_period_index.py
@@ -970,6 +970,23 @@ def test_resample_t_l_deprecated(self):
             result = ser.resample("T").mean()
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize(
+        "offset",
+        [
+            offsets.MonthBegin(),
+            offsets.BYearBegin(2),
+            offsets.BusinessHour(2),
+        ],
+    )
+    def test_asfreq_invalid_period_freq(self, offset, series_and_frame):
+        # GH#9586
+        msg = f"Invalid offset: '{offset.base}' for converting time series "
+        "with PeriodIndex."
+
+        df = series_and_frame
+        with pytest.raises(ValueError, match=msg):
+            df.asfreq(freq=offset)
+
 
 @pytest.mark.parametrize(
     "freq,freq_depr",

From fc1ab4f45b510d2ba09dcbac0467ca2801167439 Mon Sep 17 00:00:00 2001
From: Natalia Mokeeva <natalia.mokeeva.de@gmail.com>
Date: Wed, 13 Dec 2023 20:44:14 +0100
Subject: [PATCH 2/2] fix pylint error

---
 pandas/tests/resample/test_period_index.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pandas/tests/resample/test_period_index.py b/pandas/tests/resample/test_period_index.py
index 9663d35587c6e..703abbca91d64 100644
--- a/pandas/tests/resample/test_period_index.py
+++ b/pandas/tests/resample/test_period_index.py
@@ -981,7 +981,6 @@ def test_resample_t_l_deprecated(self):
     def test_asfreq_invalid_period_freq(self, offset, series_and_frame):
         # GH#9586
         msg = f"Invalid offset: '{offset.base}' for converting time series "
-        "with PeriodIndex."
 
         df = series_and_frame
         with pytest.raises(ValueError, match=msg):