Implement allow_duplicates parameter

pandas/core/frame.py

@@ -5571,6 +5571,7 @@ def reset_index(
         inplace: Literal[False] = ...,
         col_level: Hashable = ...,
         col_fill: Hashable = ...,
+        allow_duplicates: bool | None = ...,
     ) -> DataFrame:
         ...
 
@@ -5582,6 +5583,7 @@ def reset_index(
         inplace: Literal[True],
         col_level: Hashable = ...,
         col_fill: Hashable = ...,
+        allow_duplicates: bool | None = ...,
     ) -> None:
         ...
 
@@ -5593,6 +5595,7 @@ def reset_index(
         inplace: Literal[True],
         col_level: Hashable = ...,
         col_fill: Hashable = ...,
+        allow_duplicates: bool | None = ...,
     ) -> None:
         ...
 
@@ -5604,6 +5607,7 @@ def reset_index(
         inplace: Literal[True],
         col_level: Hashable = ...,
         col_fill: Hashable = ...,
+        allow_duplicates: bool | None = ...,
     ) -> None:
         ...
 
@@ -5614,6 +5618,7 @@ def reset_index(
         inplace: Literal[True],
         col_level: Hashable = ...,
         col_fill: Hashable = ...,
+        allow_duplicates: bool | None = ...,
     ) -> None:
         ...
 
@@ -5625,6 +5630,7 @@ def reset_index(
         inplace: bool = ...,
         col_level: Hashable = ...,
         col_fill: Hashable = ...,
+        allow_duplicates: bool | None = ...,
     ) -> DataFrame | None:
         ...
 
@@ -5636,6 +5642,7 @@ def reset_index(
         inplace: bool = False,
         col_level: Hashable = 0,
         col_fill: Hashable = "",
+        allow_duplicates: bool | None = False,
     ) -> DataFrame | None:
         """
         Reset the index, or a level of it.
@@ -5838,11 +5845,14 @@ class    max    type
                         level_values, lab, allow_fill=True, fill_value=lev._na_value
                     )
 
+                if allow_duplicates is None:
+                    allow_duplicates = self.flags.allows_duplicate_labels
+
                 new_obj.insert(
                     0,
                     name,
                     level_values,
-                    allow_duplicates=self.flags.allows_duplicate_labels,
+                    allow_duplicates=allow_duplicates,
                 )
 
         new_obj.index = new_index

pandas/core/series.py

@@ -1350,7 +1350,7 @@ def repeat(self, repeats, axis=None) -> Series:
         )
 
     @deprecate_nonkeyword_arguments(version=None, allowed_args=["self", "level"])
-    def reset_index(self, level=None, drop=False, name=lib.no_default, inplace=False):
+    def reset_index(self, level=None, drop=False, name=lib.no_default, inplace=False, allow_duplicates: bool = False):
         """
         Generate a new DataFrame or Series with the index reset.
 
@@ -1488,7 +1488,7 @@ def reset_index(self, level=None, drop=False, name=lib.no_default, inplace=False
                     name = self.name
 
             df = self.to_frame(name)
-            return df.reset_index(level=level, drop=drop)
+            return df.reset_index(level=level, drop=drop, allow_duplicates=allow_duplicates)
 
     # ----------------------------------------------------------------------
     # Rendering Methods

pandas/tests/frame/methods/test_reset_index.py

@@ -328,13 +328,21 @@ def test_reset_index_multiindex_nan(self):
     )
     def test_reset_index_with_datetimeindex_cols(self, name):
         # GH#5818
+        warn = None
+        if isinstance(name, Timestamp) and name.tz is not None:
+            # _deprecate_mismatched_indexing
+            warn = FutureWarning
+
         df = DataFrame(
             [[1, 2], [3, 4]],
             columns=date_range("1/1/2013", "1/2/2013"),
             index=["A", "B"],
         )
         df.index.name = name
-        result = df.reset_index()
+
+        with tm.assert_produces_warning(warn):
+            result = df.reset_index()
+
         item = name if name is not None else "index"
         columns = Index([item, datetime(2013, 1, 1), datetime(2013, 1, 2)])
         if isinstance(item, str) and item == "2012-12-31":
@@ -366,8 +374,13 @@ def test_reset_index_multiindex_columns(self):
         result = df[["B"]].rename_axis("A").reset_index()
         tm.assert_frame_equal(result, df)
 
+        # GH#16120: already existing column
+        msg = r"cannot insert \('A', ''\), already exists"    
+        with pytest.raises(ValueError, match=msg):
+            df.rename_axis("A").reset_index()    
+
         # GH#44755 reset_index with duplicate column labels
-        result = df.rename_axis("A").reset_index()
+        result = df.rename_axis("A").reset_index(allow_duplicates=True)
         levels = [["A", ""], ["A", ""], ["B", "b"]]
         expected = DataFrame(
             [[0, 0, 2], [1, 1, 3]], columns=MultiIndex.from_tuples(levels)

pandas/tests/io/pytables/test_put.py

@@ -351,7 +351,7 @@ def make_index(names=None):
             columns=["a", "b"],
             index=make_index(["date", "a", "t"]),
         )
-        msg = "cannot reindex on an axis with duplicate labels"
+        msg = "duplicate names/columns in the multi-index when storing as a table"
         with pytest.raises(ValueError, match=msg):
             store.append("df", df)
 

pandas/tests/series/methods/test_reset_index.py

@@ -195,9 +195,14 @@ def test_reset_index_dtypes_on_empty_series_with_multiindex(array, dtype):
         (["level_1", None], ["level_1", "level_1"]),
     ],
 )
-def test_column_name_duplicates(names, expected_names):
+@pytest.mark.parametrize("allow_duplicates", [False, True])
+def test_column_name_duplicates(names, expected_names, allow_duplicates):
     # GH#44755 reset_index with duplicate column labels
     s = Series([1], index=MultiIndex.from_arrays([[1], [1]], names=names))
-    result = s.reset_index()
-    expected = DataFrame([[1, 1, 1]], columns=expected_names + [0])
-    tm.assert_frame_equal(result, expected)
+    if allow_duplicates:
+        result = s.reset_index(allow_duplicates=allow_duplicates)
+        expected = DataFrame([[1, 1, 1]], columns=expected_names + [0])
+        tm.assert_frame_equal(result, expected)
+    else:
+        with pytest.raises(ValueError, match="cannot insert"):
+            s.reset_index(allow_duplicates=allow_duplicates)