ENH: Add insert_level method to MultiIndex with formatting fixes

Author: cloudboat

pandas/core/indexes/multi.py

@@ -4452,46 +4452,4 @@ def cartesian_product(X: list[np.ndarray]) -> list[np.ndarray]:
         for i, x in enumerate(X)
     ]
 
-    def insert_level(self, position: int, value, name=None):
-        """
-        Insert a new level at the specified position in the MultiIndex.
-        """
-        if not isinstance(position, int):
-            raise TypeError("position must be an integer")
-
-        if position < 0 or position > self.nlevels:
-            raise ValueError(f"position must be between 0 and {self.nlevels}")
-
-        from pandas.core.construction import extract_array
-        from pandas.core.indexes.base import ensure_index
-
-        if not hasattr(value, '__iter__') or isinstance(value, str):
-            value = [value] * len(self)
-        else:
-            value = list(value)
-            if len(value) != len(self):
-                raise ValueError("Length of values must match length of index")
-
-        tuples = list(self)
-
-        new_tuples = []
-        for i, tup in enumerate(tuples):
-            if isinstance(tup, tuple):
-                new_tuple = list(tup)
-                new_tuple.insert(position, value[i])
-                new_tuples.append(tuple(new_tuple))
-            else:
-                new_tuple = [tup]
-                new_tuple.insert(position, value[i])
-                new_tuples.append(tuple(new_tuple))
-
-        if self.names is not None:
-            new_names = list(self.names)
-        else:
-            new_names = [None] * self.nlevels
-
-        new_names.insert(position, name)
-
-        from pandas import MultiIndex
-        return MultiIndex.from_tuples(new_tuples, names=new_names)
 

pandas/tests/indexes/multi/test_insert_level.py

@@ -1,62 +1,61 @@
 import pytest
+
 import pandas as pd
-import numpy as np
 import pandas._testing as tm
 
 
-
 class TestMultiIndexInsertLevel:
 
     def setup_method(self):
         self.simple_idx = pd.MultiIndex.from_tuples(
-            [('A', 1), ('B', 2), ('C', 3)], names=['level1', 'level2']
+            [("A", 1), ("B", 2), ("C", 3)], names=["level1", "level2"]
         )
-        self.empty_idx = pd.MultiIndex.from_tuples([], names=['level1', 'level2'])
+        self.empty_idx = pd.MultiIndex.from_tuples([], names=["level1", "level2"])
 
     def test_insert_level_basic(self):
-        result = self.simple_idx.insert_level(0, 'new_value')
+        result = self.simple_idx.insert_level(0, "new_value")
         expected = pd.MultiIndex.from_tuples(
-            [('new_value', 'A', 1), ('new_value', 'B', 2), ('new_value', 'C', 3)],
-            names=[None, 'level1', 'level2']
+            [("new_value", "A", 1), ("new_value", "B", 2), ("new_value", "C", 3)],
+            names=[None, "level1", "level2"]
         )
         tm.assert_index_equal(result, expected)
 
-        result = self.simple_idx.insert_level(1, 'middle')
+        result = self.simple_idx.insert_level(1, "middle")
         expected = pd.MultiIndex.from_tuples(
-            [('A', 'middle', 1), ('B', 'middle', 2), ('C', 'middle', 3)],
-            names=['level1', None, 'level2']
+            [("A", "middle", 1), ("B", "middle", 2), ("C", "middle", 3)],
+            names=["level1", None, "level2"]
         )
         tm.assert_index_equal(result, expected)
 
     def test_insert_level_with_different_values(self):
-        new_values = ['X', 'Y', 'Z']
+        new_values = ["X", "Y", "Z"]
         result = self.simple_idx.insert_level(1, new_values)
         expected = pd.MultiIndex.from_tuples(
-            [('A', 'X', 1), ('B', 'Y', 2), ('C', 'Z', 3)],
-            names=['level1', None, 'level2']
+            [("A", "X", 1), ("B", "Y", 2), ("C", "Z", 3)],
+            names=["level1", None, "level2"]
         )
         tm.assert_index_equal(result, expected)
 
     def test_insert_level_with_name(self):
-        result = self.simple_idx.insert_level(0, 'new_val', name='new_level')
-        assert result.names[0] == 'new_level'
+        result = self.simple_idx.insert_level(0, "new_val", name="new_level")
+        assert result.names[0] == "new_level"
 
     def test_insert_level_edge_positions(self):
-        result_start = self.simple_idx.insert_level(0, 'start')
+        result_start = self.simple_idx.insert_level(0, "start")
         assert result_start.nlevels == 3
 
-        result_end = self.simple_idx.insert_level(2, 'end')
+        result_end = self.simple_idx.insert_level(2, "end")
         assert result_end.nlevels == 3
 
     def test_insert_level_error_cases(self):
         with pytest.raises(ValueError, match="position must be between"):
-            self.simple_idx.insert_level(5, 'invalid')
+            self.simple_idx.insert_level(5, "invalid")
 
         with pytest.raises(ValueError, match="position must be between"):
-            self.simple_idx.insert_level(-1, 'invalid')
+            self.simple_idx.insert_level(-1, "invalid")
 
         with pytest.raises(ValueError, match="Length of values must match"):
-            self.simple_idx.insert_level(1, ['too', 'few'])
+            self.simple_idx.insert_level(1, ["too", "few"])
 
     def test_insert_level_with_different_data_types(self):
         result_int = self.simple_idx.insert_level(1, 100)
@@ -71,24 +70,24 @@ def test_insert_level_with_different_data_types(self):
 
     def test_insert_level_preserves_original(self):
         original = self.simple_idx.copy()
-        result = self.simple_idx.insert_level(1, 'temp')
+        result = self.simple_idx.insert_level(1, "temp")
 
         tm.assert_index_equal(original, self.simple_idx)
 
         assert result.nlevels == original.nlevels + 1
 
         def test_debug_names():
             idx = pd.MultiIndex.from_tuples(
-                [('A', 1), ('B', 2), ('C', 3)],
-                names=['level1', 'level2']
+                [("A", 1), ("B", 2), ("C", 3)],
+                names=["level1", "level2"]
             )
             print("Original names:", idx.names)
 
-            result = idx.insert_level(0, 'new_value')
+            result = idx.insert_level(0, "new_value")
             print("Result names:", result.names)
 
             expected = pd.MultiIndex.from_tuples(
-                [('new_value', 'A', 1), ('new_value', 'B', 2), ('new_value', 'C', 3)],
-                names=[None, 'level1', 'level2']
+                [("new_value", "A", 1), ("new_value", "B", 2), ("new_value", "C", 3)],
+                names=[None, "level1", "level2"]
             )
-            print("Expected names:", expected.names)
+            print("Expected names:", expected.names)