bpo-42202: Store func annotations as a tuple (GH-23316)

Reduce memory footprint and improve performance of loading modules having many func annotations.

  >>> sys.getsizeof({"a":"int","b":"int","return":"int"})
  232
  >>> sys.getsizeof(("a","int","b","int","return","int"))
  88

The tuple is converted into dict on the fly when `func.__annotations__` is accessed first.

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Inada Naoki <songofacandy@gmail.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/Objects/funcobject.c b/Objects/funcobject.c
index 9b4302a..e7961b3 100644
--- a/Objects/funcobject.c
+++ b/Objects/funcobject.c
@@ -424,6 +424,25 @@ func_get_annotations(PyFunctionObject *op, void *Py_UNUSED(ignored))
         if (op->func_annotations == NULL)
             return NULL;
     }
+    if (PyTuple_CheckExact(op->func_annotations)) {
+        PyObject *ann_tuple = op->func_annotations;
+        PyObject *ann_dict = PyDict_New();
+        if (ann_dict == NULL) {
+            return NULL;
+        }
+
+        assert(PyTuple_GET_SIZE(ann_tuple) % 2 == 0);
+
+        for (Py_ssize_t i = 0; i < PyTuple_GET_SIZE(ann_tuple); i += 2) {
+            int err = PyDict_SetItem(ann_dict,
+                                     PyTuple_GET_ITEM(ann_tuple, i),
+                                     PyTuple_GET_ITEM(ann_tuple, i + 1));
+
+            if (err < 0)
+                return NULL;
+        }
+        Py_SETREF(op->func_annotations, ann_dict);
+    }
     Py_INCREF(op->func_annotations);
     return op->func_annotations;
 }