added UserWarnings if max_epochs not set in the Trainer class (#10700)

CHANGELOG.md

@@ -39,6 +39,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Added `LightningCLI.configure_optimizers` to override the `configure_optimizers` return value ([#10860](https://github.com/PyTorchLightning/pytorch-lightning/issues/10860))
 
+
+- Added a warning that shows when `max_epochs` in the `Trainer` is not set ([#10700](https://github.com/PyTorchLightning/pytorch-lightning/issues/10700))
+
+
 ### Changed
 
 - Raised exception in `init_dist_connection()` when torch distibuted is not available ([#10418](https://github.com/PyTorchLightning/pytorch-lightning/issues/10418))

pytorch_lightning/loops/utilities.py

@@ -13,8 +13,9 @@
 # limitations under the License.
 from collections import OrderedDict
 from contextlib import contextmanager
+from datetime import timedelta
 from functools import lru_cache
-from typing import Any, Dict, Generator, Iterator, List, Optional, Sequence, Tuple
+from typing import Any, Dict, Generator, Iterator, List, Optional, Sequence, Tuple, Union
 
 import numpy as np
 import torch
@@ -22,11 +23,13 @@ from torch.optim import Optimizer
 
 import pytorch_lightning as pl
 from pytorch_lightning.plugins import ParallelPlugin
+from pytorch_lightning.utilities import rank_zero_warn
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.fetching import AbstractDataFetcher, DataLoaderIterDataFetcher
 from pytorch_lightning.utilities.memory import recursive_detach
 from pytorch_lightning.utilities.signature_utils import is_param_in_hook_signature
 from pytorch_lightning.utilities.types import STEP_OUTPUT
+from pytorch_lightning.utilities.warnings import PossibleUserWarning
 
 
 def check_finite_loss(loss: Optional[torch.Tensor]) -> None:
@@ -61,6 +64,40 @@ def _extract_hiddens(training_step_output: STEP_OUTPUT, truncated_bptt_steps: in
     return hiddens
 
 
+def _parse_loop_limits(
+    min_steps: Optional[int],
+    max_steps: int,
+    min_epochs: Optional[int],
+    max_epochs: int,
+    max_time: Optional[Union[str, timedelta, Dict[str, int]]],
+) -> Tuple[Optional[int], int, Optional[int], int, Optional[Union[str, timedelta, Dict[str, int]]]]:
+    """This utility computes the default values for the minimum and maximum number of steps and epochs given the
+    values the user has selected.
+
+    Args:
+        min_steps: Minimum number of steps.
+        max_steps: Maximum number of steps.
+        min_epochs: Minimum number of epochs.
+        max_epochs: Maximum number of epochs.
+        max_time: Maximum time for the training.
+
+    Returns:
+        The parsed limits, with default values being set for the ones that the user did not specify.
+    """
+    if max_epochs is None:
+        if max_steps == -1 and max_time is None:
+            rank_zero_warn(
+                "`max_epochs` was not set. Setting it to 1000 epochs. To train without an epoch limit,"
+                " set `max_epochs=-1`.",
+                category=PossibleUserWarning,
+            )
+            max_epochs = 1000
+        else:
+            max_epochs = -1
+    min_epochs = 1 if (min_epochs is None and min_steps is None and max_time is None) else min_epochs
+    return min_steps, max_steps, min_epochs, max_epochs, max_time
+
+
 def _build_training_step_kwargs(
     lightning_module: "pl.LightningModule",
     optimizers: Sequence[Optimizer],

pytorch_lightning/trainer/trainer.py

@@ -38,6 +38,7 @@ from pytorch_lightning.loggers.tensorboard import TensorBoardLogger
 from pytorch_lightning.loops import PredictionLoop, TrainingBatchLoop, TrainingEpochLoop
 from pytorch_lightning.loops.dataloader.evaluation_loop import EvaluationLoop
 from pytorch_lightning.loops.fit_loop import FitLoop
+from pytorch_lightning.loops.utilities import _parse_loop_limits
 from pytorch_lightning.plugins import (
     ApexMixedPrecisionPlugin,
     DDPSpawnPlugin,
@@ -455,13 +456,11 @@ class Trainer(
         self.signal_connector = SignalConnector(self)
         self.tuner = Tuner(self)
 
-        fit_loop = FitLoop(
+        min_steps, max_steps, min_epochs, max_epochs, max_time = _parse_loop_limits(
-            min_epochs=(1 if (min_epochs is None and min_steps is None and max_time is None) else min_epochs),
+            min_steps, max_steps, min_epochs, max_epochs, max_time
-            max_epochs=(
-                max_epochs if max_epochs is not None else (1000 if (max_steps == -1 and max_time is None) else -1)
-            ),
         )
-        training_epoch_loop = TrainingEpochLoop(min_steps, max_steps)
+        fit_loop = FitLoop(min_epochs=min_epochs, max_epochs=max_epochs)
+        training_epoch_loop = TrainingEpochLoop(min_steps=min_steps, max_steps=max_steps)
         training_batch_loop = TrainingBatchLoop()
         training_validation_loop = EvaluationLoop()
         training_epoch_loop.connect(batch_loop=training_batch_loop, val_loop=training_validation_loop)

tests/accelerators/test_ipu.py

@@ -120,7 +120,7 @@ def test_warning_if_ipus_not_used(tmpdir):
 @RunIf(ipu=True)
 def test_no_warning_plugin(tmpdir):
     with pytest.warns(None) as record:
-        Trainer(default_root_dir=tmpdir, strategy=IPUPlugin(training_opts=poptorch.Options()))
+        Trainer(default_root_dir=tmpdir, max_epochs=1, strategy=IPUPlugin(training_opts=poptorch.Options()))
     assert len(record) == 0
 
 

tests/trainer/flags/test_min_max_epochs.py

@@ -1,6 +1,7 @@
 import pytest
 
 from pytorch_lightning import Trainer
+from pytorch_lightning.utilities.warnings import PossibleUserWarning
 from tests.helpers import BoringModel
 
 
@@ -33,3 +34,10 @@ def test_min_max_steps_epochs(tmpdir, min_epochs, max_epochs, min_steps, max_ste
     # check training stopped at max_epochs or max_steps
     if trainer.max_steps and not trainer.max_epochs:
         assert trainer.global_step == trainer.max_steps
+
+
+def test_max_epochs_not_set_warning():
+    """Test that a warning is emitted when `max_epochs` was not set by the user."""
+    with pytest.warns(PossibleUserWarning, match="`max_epochs` was not set. Setting it to 1000 epochs."):
+        trainer = Trainer(max_epochs=None)
+        assert trainer.max_epochs == 1000