Fix Metric.__iter__ by setting it to None

CHANGELOG.md

@@ -43,6 +43,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Extend `EnumStr` raising `ValueError` for invalid value ([#1479](https://github.com/Lightning-AI/metrics/pull/1479))
 
 
+- Changed `__iter__` method from raising `NotImplementedError` to `TypeError` by setting to `None` ([#1538](https://github.com/Lightning-AI/metrics/pull/1538))
+
 ### Deprecated
 
 -
@@ -64,7 +66,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed `multilabel` in `ExactMatch` ([#1474](https://github.com/Lightning-AI/metrics/pull/1474))
 
 
-
 ## [0.11.1] - 2023-01-30
 
 ### Fixed

src/torchmetrics/metric.py

@@ -920,9 +920,7 @@ def __getnewargs__(self) -> Tuple:
         """Needede method for construction of new metrics __new__ method."""
         return (Metric.__str__(self),)
 
-    def __iter__(self):
-        """Iteration over metrics are not allowed. Use metric collections for nesting metrics."""
-        raise NotImplementedError("Metrics does not support iteration.")
+    __iter__ = None
 
 
 def _neg(x: Tensor) -> Tensor:

tests/unittests/bases/test_metric.py

@@ -468,7 +468,7 @@ def test_custom_availability_check_and_sync_fn():
 
 def test_no_iteration_allowed():
     metric = DummyMetric()
-    with pytest.raises(NotImplementedError, match="Metrics does not support iteration."):  # noqa: PT012
+    with pytest.raises(TypeError, match="'DummyMetric' object is not iterable"):  # noqa: PT012
         for m in metric:
             continue