Improve performance

Author: Roger Thomas

pandas/core/frame.py

@@ -1846,30 +1846,29 @@ def _to_dict_helper(self, orient, into_c, into):
         elif orient == "index":
             if not self.index.is_unique:
                 raise ValueError("DataFrame index must be unique for orient='index'.")
+            columns = self.columns.tolist()
             if object_dtype_cols:
                 is_object_dtype_by_index = [
                     col in object_dtype_cols for col in self.columns
                 ]
                 return into_c(
                     (
                         t[0],
-                        dict(
-                            zip(
-                                self.columns,
-                                [
-                                    maybe_box_native(v)
-                                    if is_object_dtype_by_index[i]
-                                    else v
-                                    for i, v in enumerate(t[1:])
-                                ],
-                            )
-                        ),
+                        {
+                            columns[i]: maybe_box_native(v)
+                            if is_object_dtype_by_index[i]
+                            else v
+                            for i, v in enumerate(t[1:])
+                        },
                     )
                     for t in self.itertuples(name=None)
                 )
             else:
                 return into_c(
-                    (t[0], dict(zip(self.columns, t[1:])))
+                    (
+                        t[0],
+                        {columns[i]: v for i, v in enumerate(t[1:])},
+                    )
                     for t in self.itertuples(name=None)
                 )
         elif orient == "tight":