Add get_default_index_names method to Index and MultiIndex

Author: gcaria

pandas/core/frame.py

@@ -5783,37 +5783,13 @@ class    max    type
             if len(level) < self.index.nlevels:
                 new_index = self.index.droplevel(level)
 
-        if names is not None:
-            if isinstance(self.index, MultiIndex):
-                if not isinstance(names, (tuple, list)):
-                    raise ValueError("Names must be a tuple or list")
-            else:
-                if not isinstance(names, str):
-                    raise ValueError("Names must be a string")
-
         if not drop:
             to_insert: Iterable[tuple[Any, Any | None]]
             if isinstance(self.index, MultiIndex):
-                if not names:
-                    names = [
-                        (n if n is not None else f"level_{i}")
-                        for i, n in enumerate(self.index.names)
-                    ]
-                else:
-
-                    if len(names) != self.index.nlevels:
-                        raise ValueError(
-                            f"The number of provided names "
-                            f"({len(names)}) does not match the number of"
-                            f" MultiIndex levels ({self.index.nlevels})"
-                        )
+                names = self.index.get_default_index_names(names)
                 to_insert = zip(self.index.levels, self.index.codes)
             else:
-                default = "index" if "index" not in self else "level_0"
-                if not names:
-                    names = [default] if self.index.name is None else [self.index.name]
-                else:
-                    names = [names]
+                names = self.index.get_default_index_names(self, names)
                 to_insert = ((self.index, None),)
 
             multi_col = isinstance(self.columns, MultiIndex)

pandas/core/indexes/base.py

@@ -1559,6 +1559,16 @@ def _validate_names(
 
         return new_names
 
+    def get_default_index_names(self, df: DataFrame, names: str = None) -> str:
+        if names is not None and not isinstance(names, str):
+            raise ValueError("Names must be a string")
+        default = "index" if "index" not in self else "level_0"
+        if not names:
+            names = [default] if df.index.name is None else [df.index.name]
+        else:
+            names = [names]
+        return names
+
     def _get_names(self) -> FrozenList:
         return FrozenList((self.name,))
 

pandas/core/indexes/multi.py

@@ -1390,6 +1390,25 @@ def format(
     # --------------------------------------------------------------------
     # Names Methods
 
+    def get_default_index_names(self, names=None):
+
+        if names is not None and not isinstance(names, (tuple, list)):
+            raise ValueError("Names must be a tuple or list")
+
+        if not names:
+            names = [
+                (n if n is not None else f"level_{i}") for i, n in enumerate(self.names)
+            ]
+        else:
+            if len(names) != self.index.nlevels:
+                raise ValueError(
+                    f"The number of provided names "
+                    f"({len(names)}) does not match the number of"
+                    f" MultiIndex levels ({self.index.nlevels})"
+                )
+
+        return names
+
     def _get_names(self) -> FrozenList:
         return FrozenList(self._names)