Backport PR #37181 on branch 1.1.x (BUG: Fix isin with read-only target)

doc/source/whatsnew/v1.1.4.rst

@@ -28,6 +28,7 @@ Fixed regressions
 Bug fixes
 ~~~~~~~~~
 - Bug causing ``groupby(...).sum()`` and similar to not preserve metadata (:issue:`29442`)
+- Bug in :meth:`Series.isin` and :meth:`DataFrame.isin` raising a ``ValueError`` when the target was read-only (:issue:`37174`)
 
 .. ---------------------------------------------------------------------------
 

pandas/_libs/hashtable_func_helper.pxi.in

@@ -208,7 +208,7 @@ def duplicated_{{dtype}}(const {{c_type}}[:] values, object keep='first'):
 {{if dtype == 'object'}}
 def ismember_{{dtype}}(ndarray[{{c_type}}] arr, ndarray[{{c_type}}] values):
 {{else}}
-def ismember_{{dtype}}(const {{c_type}}[:] arr, {{c_type}}[:] values):
+def ismember_{{dtype}}(const {{c_type}}[:] arr, const {{c_type}}[:] values):
 {{endif}}
     """
     Return boolean of values in arr on an

pandas/tests/frame/methods/test_isin.py

@@ -204,3 +204,12 @@ def test_isin_category_frame(self, values):
 
         result = df.isin(values)
         tm.assert_frame_equal(result, expected)
+
+    def test_isin_read_only(self):
+        # https://github.com/pandas-dev/pandas/issues/37174
+        arr = np.array([1, 2, 3])
+        arr.setflags(write=False)
+        df = DataFrame([1, 2, 3])
+        result = df.isin(arr)
+        expected = DataFrame([True, True, True])
+        tm.assert_frame_equal(result, expected)

pandas/tests/series/methods/test_isin.py

@@ -80,3 +80,12 @@ def test_isin_empty(self, empty):
 
         result = s.isin(empty)
         tm.assert_series_equal(expected, result)
+
+    def test_isin_read_only(self):
+        # https://github.com/pandas-dev/pandas/issues/37174
+        arr = np.array([1, 2, 3])
+        arr.setflags(write=False)
+        s = Series([1, 2, 3])
+        result = s.isin(arr)
+        expected = Series([True, True, True])
+        tm.assert_series_equal(result, expected)