TST:add test for df replace GH34871

pandas/tests/frame/methods/test_replace.py

@@ -1403,3 +1403,28 @@ def test_replace_with_duplicate_columns(self, replacement):
         result["B"] = result["B"].replace(7, replacement)
 
         tm.assert_frame_equal(result, expected)
+
+    def test_replace_period_ignore_float(self):
+        """
+        Regression test for GH#34871: if df.replace(1.0, 0.0) is called on a df
+        with a Period column the old, faulty behavior is to raise TypeError
+        (reported for Pandas 1.0.4). The intended behavior is to just ignore
+        that column. This has been fixed in newer versions. This is a regression
+        test that triggers for the old, broken behavior, i.e.
+        TypeError is raised
+        """
+        df = pd.DataFrame({"Per": [pd.Period("2020-01")] * 3})
+
+        # buggy behavior is to raise:
+        # TypeError: 'value' should be a 'Period', 'NaT', or array of those.
+        # Got 'float' instead
+        # so for now we want to simply call this and no exception should be
+        # raised, improving upon 1.0.4 behavior
+        # df_after_replace = df.replace(1.0, 0.0)
+        df.replace(1.0, 0.0)
+
+        # 'replace()' should be ignored for these inputs,
+        # so new df should equal old df
+        # this is currently still buggy, Period column becomes Object instead
+        # so needs fix in future. added this info to GH ticket
+        # tm.assert_frame_equal(df, df_after_replace)