Prevent iteration over metrics (#1320)

* fix

* changelog

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -46,6 +46,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed bug in `Metrictracker.best_metric` when `return_step=False` ([#1306](https://github.com/Lightning-AI/metrics/pull/1306))
 
 
+- Fixed bug to prevent users from going into a infinite loop if trying to iterate of a single metric ([#1320](https://github.com/Lightning-AI/metrics/pull/1320))
+
+
 ## [0.10.2] - 2022-10-31
 
 ### Changed

src/torchmetrics/metric.py

@@ -858,6 +858,9 @@ def __getitem__(self, idx: int) -> "Metric":
  def __getnewargs__(self) -> Tuple:
  return (Metric.__str__(self),)
 
+ def __iter__(self):
+ raise NotImplementedError("Metrics does not support iteration.")
+
 
 def _neg(x: Tensor) -> Tensor:
  return -torch.abs(x)

tests/unittests/bases/test_metric.py

@@ -464,3 +464,10 @@ def test_custom_availability_check_and_sync_fn():
  acc.compute()
  dummy_availability_check.assert_called_once()
  assert dummy_dist_sync_fn.call_count == 4 # tp, fp, tn, fn
+
+
+def test_no_iteration_allowed():
+ metric = DummyMetric()
+ with pytest.raises(NotImplementedError, match="Metrics does not support iteration."):
+ for m in metric:
+ continue