REF: Don't materialize range if not needed (pandas-dev#57857)

Author: mroeschke

pandas/core/groupby/groupby.py

@@ -2686,7 +2686,7 @@ def _value_counts(
             names = result_series.index.names
             # GH#55951 - Temporarily replace names in case they are integers
             result_series.index.names = range(len(names))
-            index_level = list(range(len(self._grouper.groupings)))
+            index_level = range(len(self._grouper.groupings))
             result_series = result_series.sort_index(
                 level=index_level, sort_remaining=False
             )

pandas/core/indexes/multi.py

@@ -921,7 +921,7 @@ def _set_levels(
 
         if level is None:
             new_levels = tuple(ensure_index(lev, copy=copy)._view() for lev in levels)
-            level_numbers = list(range(len(new_levels)))
+            level_numbers: range | list[int] = range(len(new_levels))
         else:
             level_numbers = [self._get_level_number(lev) for lev in level]
             new_levels_list = list(self._levels)
@@ -3014,7 +3014,7 @@ def _maybe_to_slice(loc):
                 raise KeyError(key) from err
             except TypeError:
                 # e.g. test_partial_slicing_with_multiindex partial string slicing
-                loc, _ = self.get_loc_level(key, list(range(self.nlevels)))
+                loc, _ = self.get_loc_level(key, range(self.nlevels))
                 return loc
 
         # -- partial selection or non-unique index
@@ -3101,7 +3101,7 @@ def get_loc_level(self, key, level: IndexLabel = 0, drop_level: bool = True):
         >>> mi.get_loc_level(["b", "e"])
         (1, None)
         """
-        if not isinstance(level, (list, tuple)):
+        if not isinstance(level, (range, list, tuple)):
             level = self._get_level_number(level)
         else:
             level = [self._get_level_number(lev) for lev in level]

pandas/core/reshape/pivot.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import itertools
 from typing import (
     TYPE_CHECKING,
     Callable,
@@ -422,7 +423,7 @@ def _all_key(key):
         row_margin = row_margin.stack()
 
         # GH#26568. Use names instead of indices in case of numeric names
-        new_order_indices = [len(cols)] + list(range(len(cols)))
+        new_order_indices = itertools.chain([len(cols)], range(len(cols)))
         new_order_names = [row_margin.index.names[i] for i in new_order_indices]
         row_margin.index = row_margin.index.reorder_levels(new_order_names)
     else:

pandas/core/sorting.py

@@ -523,13 +523,13 @@ def _ensure_key_mapped_multiindex(
 
     if level is not None:
         if isinstance(level, (str, int)):
-            sort_levels = [level]
+            level_iter = [level]
         else:
-            sort_levels = level
+            level_iter = level
 
-        sort_levels = [index._get_level_number(lev) for lev in sort_levels]
+        sort_levels: range | set = {index._get_level_number(lev) for lev in level_iter}
     else:
-        sort_levels = list(range(index.nlevels))  # satisfies mypy
+        sort_levels = range(index.nlevels)
 
     mapped = [
         ensure_key_mapped(index._get_level_values(level), key)

pandas/io/common.py

@@ -1223,12 +1223,14 @@ def is_potential_multi_index(
     bool : Whether or not columns could become a MultiIndex
     """
     if index_col is None or isinstance(index_col, bool):
-        index_col = []
+        index_columns = set()
+    else:
+        index_columns = set(index_col)
 
     return bool(
         len(columns)
         and not isinstance(columns, ABCMultiIndex)
-        and all(isinstance(c, tuple) for c in columns if c not in list(index_col))
+        and all(isinstance(c, tuple) for c in columns if c not in index_columns)
     )
 
 

pandas/io/parsers/readers.py

@@ -1482,7 +1482,7 @@ def _clean_options(
                 )
         else:
             if is_integer(skiprows):
-                skiprows = list(range(skiprows))
+                skiprows = range(skiprows)
             if skiprows is None:
                 skiprows = set()
             elif not callable(skiprows):