better performance for slices

Author: topper-123

pandas/core/indexes/range.py

@@ -604,7 +604,10 @@ def __getitem__(self, key):
         """
         Conserve RangeIndex type for scalar and slice keys.
         """
-        if is_scalar(key):
+        if isinstance(key, slice):
+            new_range = self._range[key]
+            return self._simple_new(new_range, name=self.name)
+        elif is_scalar(key):
             if not lib.is_integer(key):
                 raise IndexError("only integers, slices (`:`), "
                                  "ellipsis (`...`), numpy.newaxis (`None`) "
@@ -617,10 +620,6 @@ def __getitem__(self, key):
                 raise IndexError("index {key} is out of bounds for axis 0 "
                                  "with size {size}".format(key=key,
                                                            size=len(self)))
-        if isinstance(key, slice):
-            new_range = self._range[key]
-            return self.from_range(new_range, name=self.name)
-
         # fall back to Int64Index
         return super().__getitem__(key)