REGR: Don't ignore compiled patterns in replace

doc/source/whatsnew/v1.1.1.rst

@@ -23,6 +23,7 @@ Fixed regressions
 - Fixed regression in ``.groupby(..).rolling(..)`` where a segfault would occur with ``center=True`` and an odd number of values (:issue:`35552`)
 - Fixed regression in :meth:`DataFrame.apply` where functions that altered the input in-place only operated on a single row (:issue:`35462`)
 - Fixed regression in ``.groupby(..).rolling(..)`` where a custom ``BaseIndexer`` would be ignored (:issue:`35557`)
+- Fixed regression in :meth:`DataFrame.replace` and :meth:`Series.replace` where compiled regular expressions would be ignored during replacement (:issue:`35680`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/internals/managers.py

@@ -1949,7 +1949,7 @@ def _check_comparison_types(
     else:
         op = np.vectorize(
             lambda x: bool(re.search(b, x))
-            if isinstance(x, str) and isinstance(b, str)
+            if isinstance(x, str) and isinstance(b, (str, re.Pattern))
             else False
         )
 

pandas/tests/frame/methods/test_replace.py

@@ -1573,3 +1573,11 @@ def test_replace_dict_category_type(self, input_category_df, expected_category_d
         result = input_df.replace({"a": "z", "obj1": "obj9", "cat1": "catX"})
 
         tm.assert_frame_equal(result, expected)
+
+    def test_replace_with_compiled_regex(self):
+        # https://github.com/pandas-dev/pandas/issues/35680
+        df = pd.DataFrame(["a", "b", "c"])
+        regex = re.compile("^a$")
+        result = df.replace({regex: "z"}, regex=True)
+        expected = pd.DataFrame(["z", "b", "c"])
+        tm.assert_frame_equal(result, expected)

pandas/tests/series/methods/test_replace.py

@@ -1,3 +1,5 @@
+import re
+
 import numpy as np
 import pytest
 
@@ -415,3 +417,11 @@ def test_replace_extension_other(self):
         # https://github.com/pandas-dev/pandas/issues/34530
         ser = pd.Series(pd.array([1, 2, 3], dtype="Int64"))
         ser.replace("", "")  # no exception
+
+    def test_replace_with_compiled_regex(self):
+        # https://github.com/pandas-dev/pandas/issues/35680
+        s = pd.Series(["a", "b", "c"])
+        regex = re.compile("^a$")
+        result = s.replace({regex: "z"}, regex=True)
+        expected = pd.Series(["z", "b", "c"])
+        tm.assert_series_equal(result, expected)