Deprecate the default `EarlyStopping` callback monitor value (#7907)

* removed monitor default value and added depreceation message

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* format change

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* requested changes

* added test

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* format changes

* typehint change

* Update CHANGELOG.md

* requested changes

* regex

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Adrian Wälchli <aedu.waelchli@gmail.com>

CHANGELOG.md

@@ -172,6 +172,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Deprecated `self.log(sync_dist_op)` in favor of `self.log(reduce_fx)`. ([#7891](https://github.com/PyTorchLightning/pytorch-lightning/pull/7891))
 
 
+- Deprecated default value of `monitor` argument in EarlyStopping callback to enforce `monitor` as a required argument ([#7907](https://github.com/PyTorchLightning/pytorch-lightning/pull/7907))
+
+
 ### Removed
 
 - Removed `ProfilerConnector` ([#7654](https://github.com/PyTorchLightning/pytorch-lightning/pull/7654))

pytorch_lightning/callbacks/early_stopping.py

@@ -26,7 +26,7 @@ import torch
 
 import pytorch_lightning as pl
 from pytorch_lightning.callbacks.base import Callback
-from pytorch_lightning.utilities import rank_zero_warn
+from pytorch_lightning.utilities import rank_zero_deprecation, rank_zero_warn
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 
 log = logging.getLogger(__name__)
@@ -88,7 +88,7 @@ class EarlyStopping(Callback):
 
     def __init__(
         self,
-        monitor: str = 'early_stop_on',
+        monitor: Optional[str] = None,
         min_delta: float = 0.0,
         patience: int = 3,
         verbose: bool = False,
@@ -100,7 +100,6 @@ class EarlyStopping(Callback):
         check_on_train_epoch_end: bool = False,
     ):
         super().__init__()
-        self.monitor = monitor
         self.min_delta = min_delta
         self.patience = patience
         self.verbose = verbose
@@ -120,6 +119,13 @@ class EarlyStopping(Callback):
         torch_inf = torch.tensor(np.Inf)
         self.best_score = torch_inf if self.monitor_op == torch.lt else -torch_inf
 
+        if monitor is None:
+            rank_zero_deprecation(
+                "The `EarlyStopping(monitor)` argument will be required starting in v1.6."
+                " For backward compatibility, setting this to `early_stop_on`."
+            )
+        self.monitor = monitor or "early_stop_on"
+
     def _validate_condition_metric(self, logs):
         monitor_val = logs.get(self.monitor)
 

tests/deprecated_api/test_remove_1-6.py

@@ -15,6 +15,7 @@
 import pytest
 
 from pytorch_lightning import Trainer
+from pytorch_lightning.callbacks.early_stopping import EarlyStopping
 from pytorch_lightning.plugins.training_type import DDPPlugin, DDPSpawnPlugin
 from tests.helpers import BoringDataModule, BoringModel
 
@@ -172,3 +173,11 @@ def test_v1_6_0_datamodule_hooks_calls(tmpdir):
     assert dm.prepare_data_calls == 1
     assert dm.setup_calls == ['fit', None]
     assert dm.teardown_calls == ['validate', 'test']
+
+
+def test_v1_6_0_early_stopping_monitor(tmpdir):
+    with pytest.deprecated_call(
+        match=r"The `EarlyStopping\(monitor\)` argument will be required starting in v1.6."
+        " For backward compatibility, setting this to `early_stop_on`."
+    ):
+        EarlyStopping()