More idiomatic example code in BaseIndexer (pandas-dev#58356)

No need to loop when NumPy supports range and array addition

Author: wjandrea

pandas/core/indexers/objects.py

@@ -53,11 +53,8 @@ class BaseIndexer:
     >>> from pandas.api.indexers import BaseIndexer
     >>> class CustomIndexer(BaseIndexer):
     ...     def get_window_bounds(self, num_values, min_periods, center, closed, step):
-    ...         start = np.empty(num_values, dtype=np.int64)
-    ...         end = np.empty(num_values, dtype=np.int64)
-    ...         for i in range(num_values):
-    ...             start[i] = i
-    ...             end[i] = i + self.window_size
+    ...         start = np.arange(num_values, dtype=np.int64)
+    ...         end = np.arange(num_values, dtype=np.int64) + self.window_size
     ...         return start, end
     >>> df = pd.DataFrame({"values": range(5)})
     >>> indexer = CustomIndexer(window_size=2)