Fixed a crash bug in MLFlow logger (#4716)

* warnings.warn doesn't accept tuples, which causes "TypeError: expected string or bytes-like object" when the execution flow gets to this warning. Fixed that.

* Try adding a mock test

* Try adding a mock test

Co-authored-by: rohitgr7 <rohitgr1998@gmail.com>
Co-authored-by: chaton <thomas@grid.ai>

pytorch_lightning/loggers/mlflow.py

@@ -17,7 +17,6 @@ MLflow Logger
 -------------
 """
 import re
-import warnings
 from argparse import Namespace
 from time import time
 from typing import Any, Dict, Optional, Union
@@ -32,7 +31,7 @@ except ModuleNotFoundError:  # pragma: no-cover
 
 from pytorch_lightning import _logger as log
 from pytorch_lightning.loggers.base import LightningLoggerBase, rank_zero_experiment
-from pytorch_lightning.utilities import rank_zero_only
+from pytorch_lightning.utilities import rank_zero_only, rank_zero_warn
 
 LOCAL_FILE_URI_PREFIX = "file:"
 
@@ -165,9 +164,11 @@ class MLFlowLogger(LightningLoggerBase):
 
             new_k = re.sub("[^a-zA-Z0-9_/. -]+", "", k)
             if k != new_k:
-                warnings.warn(("MLFlow only allows '_', '/', '.' and ' ' special characters in metric name.\n",
-                               f"Replacing {k} with {new_k}."))
-            k = new_k
+                rank_zero_warn(
+                    "MLFlow only allows '_', '/', '.' and ' ' special characters in metric name."
+                    f" Replacing {k} with {new_k}.", RuntimeWarning
+                )
+                k = new_k
 
             self.experiment.log_metric(self.run_id, k, v, timestamp_ms, step)
 

tests/loggers/test_mlflow.py

@@ -150,8 +150,24 @@ def test_mlflow_logger_dirs_creation(tmpdir):
 @mock.patch('pytorch_lightning.loggers.mlflow.mlflow')
 @mock.patch('pytorch_lightning.loggers.mlflow.MlflowClient')
 def test_mlflow_experiment_id_retrieved_once(client, mlflow, tmpdir):
+    """
+    Test that the logger experiment_id retrieved only once.
+    """
     logger = MLFlowLogger('test', save_dir=tmpdir)
     _ = logger.experiment
     _ = logger.experiment
     _ = logger.experiment
     assert logger.experiment.get_experiment_by_name.call_count == 1
+
+
+@mock.patch('pytorch_lightning.loggers.mlflow.mlflow')
+@mock.patch('pytorch_lightning.loggers.mlflow.MlflowClient')
+def test_mlflow_logger_with_unexpected_characters(client, mlflow, tmpdir):
+    """
+    Test that the logger raises warning with special characters not accepted by MLFlow.
+    """
+    logger = MLFlowLogger('test', save_dir=tmpdir)
+    metrics = {'[some_metric]': 10}
+
+    with pytest.warns(RuntimeWarning, match='special characters in metric name'):
+        logger.log_metrics(metrics)