Prevent iteration over metrics (#1320)

* fix

* changelog

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

(cherry picked from commit 00bb1ed)

CHANGELOG.md

@@ -6,6 +6,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 **Note: we move fast, but still we preserve 0.1 version (one feature release) back compatibility.**
 
+## [unReleased] - 2022-MM-DD
+
+### Fixed
+
+- 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))
+
+
+- Fixed bug in `Metrictracker.best_metric` when `return_step=False` ([#1306](https://github.com/Lightning-AI/metrics/pull/1306))
+
 
 ## [0.10.2] - 2022-10-31
 
@@ -21,9 +33,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed restrictive dtype checking in `spearman_corrcoef` when used with autocast ([#1303](https://github.com/Lightning-AI/metrics/pull/1303))
 
 
-- Fixed bug in `Metrictracker.best_metric` when `return_step=False` ([#1306](https://github.com/Lightning-AI/metrics/pull/1306))
-
-
 ## [0.10.1] - 2022-10-21
 
 ### Fixed

src/torchmetrics/metric.py

@@ -851,6 +851,9 @@ 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

@@ -453,3 +453,10 @@ def forward(self, *args, **kwargs):
         match="Torchmetrics v0.9 introduced a new argument class property called.*",
     ):
         UnsetProperty()
+
+
+def test_no_iteration_allowed():
+    metric = DummyMetric()
+    with pytest.raises(NotImplementedError, match="Metrics does not support iteration."):
+        for m in metric:
+            continue