PERF: Optimize MultiIndex.insert_level to avoid unnecessary type conversions & REF: Remove unnecessary else branch in MultiIndex.insert_level & REF: Simplify names handling in MultiIndex.insert_level

Author: cloudboat

pandas/core/indexes/multi.py

@@ -2710,38 +2710,7 @@ def reorder_levels(self, order) -> MultiIndex:
         result = self._reorder_ilevels(order)
         return result
 
-    def insert_level(self, position: int, value, name=None) -> MultiIndex:
-        """
-        Insert a new level at the specified position and return a new MultiIndex.
-
-        Parameters
-        ----------
-        position : int
-            The integer position where the new level should be inserted.
-            Must be between 0 and ``self.nlevels`` (inclusive).
-        value : scalar or sequence
-            Values for the inserted level. If a scalar is provided, it is
-            broadcast to the length of the index. If a sequence is provided,
-            it must be the same length as the index.
-        name : Hashable, default None
-            Name of the inserted level. If not provided, the inserted level
-            name will be ``None``.
-
-        Returns
-        -------
-        MultiIndex
-            A new ``MultiIndex`` with the inserted level.
-
-        Examples
-        --------
-        >>> idx = pd.MultiIndex.from_tuples([("A", 1), ("B", 2)], names=["x", "y"])
-        >>> idx.insert_level(0, "grp")
-        MultiIndex([('grp', 'A', 1), ('grp', 'B', 2)],
-                   names=[None, 'x', 'y'])
-        >>> idx.insert_level(1, ["L1", "L2"], name="z")
-        MultiIndex([('A', 'L1', 1), ('B', 'L2', 2)],
-                   names=['x', 'z', 'y'])
-        """
+    def insert_level(self, position: int, value, name=None):
         if not isinstance(position, int):
             raise TypeError("position must be an integer")
 
@@ -2755,25 +2724,17 @@ def insert_level(self, position: int, value, name=None) -> MultiIndex:
             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))
+        for i, tup in enumerate(self):
+            if position == 0:
+                new_tuple = (value[i],) + tup
+            elif position == len(tup):
+                new_tuple = tup + (value[i],)
             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_tuple = tup[:position] + (value[i],) + tup[position:]
+            new_tuples.append(new_tuple)
 
-        new_names.insert(position, name)
+        new_names = self.names[:position] + [name] + self.names[position:]
 
         return MultiIndex.from_tuples(new_tuples, names=new_names)