optimized ListConfig iterator

news/532.feature

@@ -0,0 +1 @@
+Optimized ListConfig iterator (550x to 150x slower than native list iterator)

omegaconf/listconfig.py

@@ -497,32 +497,31 @@ def __hash__(self) -> int:
     def __iter__(self) -> Iterator[Any]:
         return self._iter_ex(resolve=True)
 
+    class ListIterator(Iterator[Any]):
+        def __init__(self, lst: Any, resolve: bool) -> None:
+            self.iter = iter(lst.__dict__["_content"])
+            self.resolve = resolve
+            self.index = 0
+
+        def __next__(self) -> Any:
+            v = next(self.iter)
+
+            if self.resolve:
+                v = v._dereference_node()
+
+            if v._is_missing():
+                raise MissingMandatoryValue(f"Missing value at index {self.index}")
+            self.index = self.index + 1
+            return _get_value(v)
+
     def _iter_ex(self, resolve: bool) -> Iterator[Any]:
         try:
             if self._is_none():
                 raise TypeError("Cannot iterate a ListConfig object representing None")
             if self._is_missing():
                 raise MissingMandatoryValue("Cannot iterate a missing ListConfig")
 
-            class MyItems(Iterator[Any]):
-                def __init__(self, lst: ListConfig) -> None:
-                    self.lst = lst
-                    self.index = 0
-
-                def __next__(self) -> Any:
-                    if self.index == len(self.lst):
-                        raise StopIteration()
-                    if resolve:
-                        v = self.lst[self.index]
-                    else:
-                        v = self.lst.__dict__["_content"][self.index]
-                        if v is not None:
-                            v = _get_value(v)
-                    self.index = self.index + 1
-                    return v
-
-            assert isinstance(self.__dict__["_content"], list)
-            return MyItems(self)
+            return ListConfig.ListIterator(self, resolve)
         except (ReadonlyConfigError, TypeError, MissingMandatoryValue) as e:
             self._format_and_raise(key=None, value=None, cause=e)
             assert False
@@ -571,15 +570,16 @@ def _set_value_impl(
         if flags is None:
             flags = {}
 
+        vk = get_value_kind(value)
         if OmegaConf.is_none(value):
             if not self._is_optional():
                 raise ValidationError(
                     "Non optional ListConfig cannot be constructed from None"
                 )
             self.__dict__["_content"] = None
-        elif get_value_kind(value) == ValueKind.MANDATORY_MISSING:
+        elif vk is ValueKind.MANDATORY_MISSING:
             self.__dict__["_content"] = "???"
-        elif get_value_kind(value) in (
+        elif vk in (
             ValueKind.INTERPOLATION,
             ValueKind.STR_INTERPOLATION,
         ):