Fix .isin Considers "1" and 1 equal

pandas/core/algorithms.py

@@ -429,7 +429,14 @@ def isin(comps: AnyArrayLike, values: AnyArrayLike) -> np.ndarray:
         # handle categoricals
         return comps.isin(values)  # type: ignore
 
-    comps, dtype = _ensure_data(comps)
+    if hasattr(comps, "dtype") and hasattr(comps.dtype, "name"):
+        if comps.dtype.name == "int64":
+            comps, dtype = _ensure_data(comps, dtype=object)
+        else:
+            comps, dtype = _ensure_data(comps)
+    else:
+        comps, dtype = _ensure_data(comps)
+
     values, _ = _ensure_data(values, dtype=dtype)
 
     # faster for larger cases to use np.in1d

pandas/tests/frame/methods/test_isin.py

@@ -189,3 +189,16 @@ def test_isin_empty_datetimelike(self):
         tm.assert_frame_equal(result, expected)
         result = df1_td.isin(df3)
         tm.assert_frame_equal(result, expected)
+
+    def test_isin_int_df_string_search(self):
+        """Comparing df with int`s (1,2) with a string at isin() ("1")
+        -> should not match values because int 1 is not equal str 1"""
+        df = DataFrame({"values": [1, 2]})
+        result = df.isin(["1"])
+        expected_false = pd.DataFrame({"values": [False, False]})
+        tm.assert_frame_equal(result, expected_false)
+
+        # Comparing df with int`s with a int at isin() -> should be fine
+        result = df.isin([1])
+        expected_true = DataFrame({"values": [True, False]})
+        tm.assert_frame_equal(result, expected_true)