Do not print empty evaluation result tables (#12427)

CHANGELOG.md

@@ -175,6 +175,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Implemented a new native and rich format in `_print_results` method of the `EvaluationLoop` ([#11332](https://github.com/PyTorchLightning/pytorch-lightning/pull/11332))
 
 
+- Do not print an empty table at the end of the `EvaluationLoop` ([#12427](https://github.com/PyTorchLightning/pytorch-lightning/pull/12427))
+
+
 - Set the `prog_bar` flag to False in `LightningModule.log_grad_norm` ([#11472](https://github.com/PyTorchLightning/pytorch-lightning/pull/11472))
 
 

pytorch_lightning/loops/dataloader/evaluation_loop.py

@@ -325,6 +325,8 @@ class EvaluationLoop(DataLoaderLoop):
         # remove the dl idx suffix
         results = [{k.split("/dataloader_idx_")[0]: v for k, v in result.items()} for result in results]
         metrics = sorted({k for keys in apply_to_collection(results, dict, EvaluationLoop._get_keys) for k in keys})
+        if not metrics:
+            return
         headers = [f"DataLoader {i}" for i in range(len(results))]
 
         # fallback is useful for testing of printed output

tests/trainer/logging_/test_eval_loop_logging.py

@@ -838,6 +838,9 @@ expected3 = """
 ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
 """
 
+inputs4 = ([{}], "foo")
+expected4 = ""
+
 
 @pytest.mark.parametrize(
     ["inputs", "expected"],
@@ -846,6 +849,7 @@ expected3 = """
         pytest.param(inputs1, expected1, id="case1"),
         pytest.param(inputs2, expected2, id="case2"),
         pytest.param(inputs3, expected3, id="case3"),
+        pytest.param(inputs4, expected4, id="empty case"),
     ],
 )
 def test_native_print_results(monkeypatch, inputs, expected):
@@ -916,6 +920,7 @@ expected3 = """
         pytest.param(inputs1, expected1, id="case1"),
         pytest.param(inputs2, expected2, id="case2"),
         pytest.param(inputs3, expected3, id="case3"),
+        pytest.param(inputs4, expected4, id="empty case"),
     ],
 )
 @RunIf(rich=True, skip_windows=True)