Changed max_steps default from None to -1

CHANGELOG.md

@@ -334,6 +334,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Updated several places in the loops and trainer to access `training_type_plugin` directly instead of `accelerator` ([#9901](https://github.com/PyTorchLightning/pytorch-lightning/pull/9901))
 
 
+- Changed default value of the `max_steps` Trainer argument from `None` to -1 ([#9460](https://github.com/PyTorchLightning/pytorch-lightning/pull/9460))
+
 
 ### Deprecated
 
@@ -408,6 +410,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Deprecated `GPUStatsMonitor` and `XLAStatsMonitor` in favor of `DeviceStatsMonitor` callback ([#9924](https://github.com/PyTorchLightning/pytorch-lightning/pull/9924))
 
+
+- Deprecated setting `Trainer(max_steps=None)`. To turn off the limit, set `Trainer(max_steps=-1)` (default) ([#9460](https://github.com/PyTorchLightning/pytorch-lightning/pull/9460))
+
+
 ### Removed
 
 - Removed deprecated `metrics` ([#8586](https://github.com/PyTorchLightning/pytorch-lightning/pull/8586/))

pytorch_lightning/loops/epoch/training_epoch_loop.py

@@ -20,15 +20,15 @@
 from pytorch_lightning import loops  # import as loops to avoid circular imports
 from pytorch_lightning.loops.batch import TrainingBatchLoop
 from pytorch_lightning.loops.batch.training_batch_loop import _OUTPUTS_TYPE as _BATCH_OUTPUTS_TYPE
-from pytorch_lightning.loops.utilities import _get_active_optimizers, _update_dataloader_iter
+from pytorch_lightning.loops.utilities import _get_active_optimizers, _is_max_limit_reached, _update_dataloader_iter
 from pytorch_lightning.trainer.connectors.logger_connector.result import ResultCollection
 from pytorch_lightning.trainer.progress import BatchProgress, SchedulerProgress
 from pytorch_lightning.utilities.apply_func import apply_to_collection
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.fetching import AbstractDataFetcher
 from pytorch_lightning.utilities.model_helpers import is_overridden
 from pytorch_lightning.utilities.signature_utils import is_param_in_hook_signature
-from pytorch_lightning.utilities.warnings import WarningCache
+from pytorch_lightning.utilities.warnings import rank_zero_deprecation, WarningCache
 
 _OUTPUTS_TYPE = List[_BATCH_OUTPUTS_TYPE]
 
@@ -41,13 +41,20 @@ class TrainingEpochLoop(loops.Loop[_OUTPUTS_TYPE]):
         max_steps: The maximum number of steps (batches) to process
     """
 
-    def __init__(self, min_steps: int, max_steps: int):
+    def __init__(self, min_steps: Optional[int] = 0, max_steps: int = -1) -> None:
         super().__init__()
-        self.min_steps: int = min_steps
-
-        if max_steps and max_steps < -1:
-            raise MisconfigurationException(f"`max_steps` must be a positive integer or -1. You passed in {max_steps}.")
-        self.max_steps: int = max_steps
+        if max_steps is None:
+            rank_zero_deprecation(
+                "Setting `max_steps = None` is deprecated in v1.5 and will no longer be supported in v1.7."
+                " Use `max_steps = -1` instead."
+            )
+            max_steps = -1
+        elif max_steps < -1:
+            raise MisconfigurationException(
+                f"`max_steps` must be a non-negative integer or -1 (infinite steps). You passed in {max_steps}."
+            )
+        self.min_steps = min_steps
+        self.max_steps = max_steps
 
         self.global_step: int = 0
         self.batch_progress = BatchProgress()
@@ -79,7 +86,7 @@ def batch_idx(self) -> int:
 
     @property
     def _is_training_done(self) -> bool:
-        max_steps_reached = self.max_steps is not None and self.global_step >= self.max_steps
+        max_steps_reached = _is_max_limit_reached(self.global_step, self.max_steps)
         return max_steps_reached or self._num_ready_batches_reached()
 
     @property

pytorch_lightning/loops/fit_loop.py

@@ -16,9 +16,11 @@
 
 from pytorch_lightning.loops import Loop
 from pytorch_lightning.loops.epoch import TrainingEpochLoop
+from pytorch_lightning.loops.utilities import _is_max_limit_reached
 from pytorch_lightning.trainer.connectors.logger_connector.result import ResultCollection
 from pytorch_lightning.trainer.progress import Progress
 from pytorch_lightning.trainer.supporters import TensorRunningAccum
+from pytorch_lightning.utilities import rank_zero_deprecation
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 
 log = logging.getLogger(__name__)
@@ -29,15 +31,19 @@ class FitLoop(Loop):
 
     Args:
         min_epochs: The minimum number of epochs
-        max_epochs: The maximum number of epochs
+        max_epochs: The maximum number of epochs, can be set -1 to turn this limit off
     """
 
-    def __init__(self, min_epochs: Optional[int] = None, max_epochs: Optional[int] = None):
+    def __init__(
+        self,
+        min_epochs: Optional[int] = 1,
+        max_epochs: int = 1000,
+    ) -> None:
         super().__init__()
-        # Allow max_epochs or max_steps to be zero, since this will be handled by fit_loop.done
-        if max_epochs and max_epochs < -1:
+        if max_epochs < -1:
+            # Allow max_epochs to be zero, since this will be handled by fit_loop.done
             raise MisconfigurationException(
-                f"`max_epochs` must be a positive integer or -1. You passed in {max_epochs}."
+                f"`max_epochs` must be a non-negative integer or -1. You passed in {max_epochs}."
             )
 
         self.max_epochs = max_epochs
@@ -102,8 +108,16 @@ def max_steps(self) -> int:
     def max_steps(self, value: int) -> None:
         """Sets the maximum number of steps (forwards to epoch_loop)"""
         # TODO(@awaelchli): This setter is required by debugging connector (fast dev run), should be avoided
-        if value and value < -1:
-            raise MisconfigurationException(f"`max_steps` must be a positive integer or -1. You passed in {value}.")
+        if value is None:
+            rank_zero_deprecation(
+                "Setting `max_steps = None` is deprecated in v1.5 and will no longer be supported in v1.7."
+                " Use `max_steps = -1` instead."
+            )
+            value = -1
+        elif value < -1:
+            raise MisconfigurationException(
+                f"`max_steps` must be a non-negative integer or -1 (infinite steps). You passed in {value}."
+            )
         self.epoch_loop.max_steps = value
 
     @property
@@ -141,8 +155,8 @@ def done(self) -> bool:
         is reached.
         """
         # TODO(@awaelchli): Move track steps inside training loop and move part of these condition inside training loop
-        stop_steps = FitLoop._is_max_limit_enabled(self.max_steps) and self.global_step >= self.max_steps
-        stop_epochs = FitLoop._is_max_limit_enabled(self.max_epochs) and self.current_epoch >= self.max_epochs
+        stop_steps = _is_max_limit_reached(self.global_step, self.max_steps)
+        stop_epochs = _is_max_limit_reached(self.current_epoch, self.max_epochs)
 
         should_stop = False
         if self.trainer.should_stop:
@@ -249,16 +263,3 @@ def teardown(self) -> None:
     def _should_accumulate(self) -> bool:
         """Whether the gradients should be accumulated."""
         return self.epoch_loop._should_accumulate()
-
-    @staticmethod
-    def _is_max_limit_enabled(max_value: Optional[int]) -> bool:
-        """Checks whether the max_value is enabled. This can be used for checking whether max_epochs or max_steps
-        is enabled.
-
-        Args:
-            max_value: the value to check
-
-        Returns:
-            whether the limit for this value should be enabled
-        """
-        return max_value not in (None, -1)

pytorch_lightning/loops/utilities.py

@@ -168,3 +168,16 @@ def _get_active_optimizers(
     # find optimizer index by looking for the first {item > current_place} in the cumsum list
     opt_idx = np.searchsorted(freq_cumsum, current_place_in_loop, side="right")
     return [(opt_idx, optimizers[opt_idx])]
+
+
+def _is_max_limit_reached(current: int, maximum: int = -1) -> bool:
+    """Check if the limit has been reached (if enabled).
+
+    Args:
+        current: the current value
+        maximum: the maximum value (or -1 to disable limit)
+
+    Returns:
+        bool: whether the limit has been reached
+    """
+    return maximum != -1 and current >= maximum

pytorch_lightning/trainer/connectors/checkpoint_connector.py

@@ -21,7 +21,7 @@
 
 import pytorch_lightning as pl
 from pytorch_lightning.loggers import LightningLoggerBase
-from pytorch_lightning.loops.fit_loop import FitLoop
+from pytorch_lightning.loops.utilities import _is_max_limit_reached
 from pytorch_lightning.trainer.states import TrainerFn
 from pytorch_lightning.utilities import _OMEGACONF_AVAILABLE, rank_zero_deprecation, rank_zero_info, rank_zero_warn
 from pytorch_lightning.utilities.cloud_io import atomic_save, get_filesystem
@@ -220,7 +220,7 @@ def restore_loops(self) -> None:
 
         # crash if max_epochs is lower then the current epoch from the checkpoint
         if (
-            FitLoop._is_max_limit_enabled(self.trainer.max_epochs)
+            self.trainer.max_epochs != -1
             and self.trainer.max_epochs is not None
             and self.trainer.current_epoch > self.trainer.max_epochs
         ):
@@ -351,7 +351,7 @@ def dump_checkpoint(self, weights_only: bool = False) -> dict:
         # dump epoch/global_step/pytorch-lightning_version
         current_epoch = self.trainer.current_epoch
         global_step = self.trainer.global_step
-        has_reached_max_steps = self.trainer.max_steps and self.trainer.max_steps <= global_step
+        has_reached_max_steps = _is_max_limit_reached(global_step, self.trainer.max_steps)
 
         global_step += 1
         if not has_reached_max_steps:

pytorch_lightning/trainer/trainer.py

@@ -145,7 +145,7 @@ def __init__(
         accumulate_grad_batches: Optional[Union[int, Dict[int, int]]] = None,
         max_epochs: Optional[int] = None,
         min_epochs: Optional[int] = None,
-        max_steps: Optional[int] = None,
+        max_steps: int = -1,
         min_steps: Optional[int] = None,
         max_time: Optional[Union[str, timedelta, Dict[str, int]]] = None,
         limit_train_batches: Union[int, float] = 1.0,
@@ -327,9 +327,9 @@ def __init__(
             min_epochs: Force training for at least these many epochs. Disabled by default (None).
                 If both min_epochs and min_steps are not specified, defaults to ``min_epochs = 1``.
 
-            max_steps: Stop training after this number of steps. Disabled by default (None). If ``max_steps = None``
-                and ``max_epochs = None``, will default to ``max_epochs = 1000``. To disable this default, set
-                ``max_steps`` to ``-1``.
+            max_steps: Stop training after this number of steps. Disabled by default (-1). If ``max_steps = -1``
+                and ``max_epochs = None``, will default to ``max_epochs = 1000``. To enable infinite training, set
+                ``max_epochs`` to ``-1``.
 
             min_steps: Force training for at least these number of steps. Disabled by default (None).
 
@@ -455,10 +455,11 @@ def __init__(
         self.signal_connector = SignalConnector(self)
         self.tuner = Tuner(self)
 
-        # max_epochs won't default to 1000 if max_steps/max_time are specified (including being set to -1).
         fit_loop = FitLoop(
             min_epochs=(1 if (min_epochs is None and min_steps is None and max_time is None) else min_epochs),
-            max_epochs=(1000 if (max_epochs is None and max_steps is None and max_time is None) else max_epochs),
+            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)
         training_batch_loop = TrainingBatchLoop()
@@ -1332,7 +1333,7 @@ def __set_ckpt_path(self, ckpt_path: Optional[str], model_provided: bool, model_
 
         if not ckpt_path:
             raise MisconfigurationException(
-                f'`.{fn}()` found no path for the best weights: "{ckpt_path}". Please'
+                f"`.{fn}()` found no path for the best weights: {ckpt_path!r}. Please"
                 f" specify a path for a checkpoint `.{fn}(ckpt_path=PATH)`"
             )
         return ckpt_path
@@ -1933,15 +1934,15 @@ def current_epoch(self) -> int:
         return self.fit_loop.current_epoch
 
     @property
-    def max_epochs(self) -> Optional[int]:
+    def max_epochs(self) -> int:
         return self.fit_loop.max_epochs
 
     @property
     def min_epochs(self) -> Optional[int]:
         return self.fit_loop.min_epochs
 
     @property
-    def max_steps(self) -> Optional[int]:
+    def max_steps(self) -> int:
         return self.fit_loop.max_steps
 
     @property

tests/callbacks/test_timer.py

@@ -49,7 +49,7 @@ def on_fit_start(self):
     timer = [c for c in trainer.callbacks if isinstance(c, Timer)][0]
     assert timer._duration == 1
     assert trainer.max_epochs == -1
-    assert trainer.max_steps is None
+    assert trainer.max_steps == -1
 
 
 @pytest.mark.parametrize(

tests/deprecated_api/test_remove_1-7.py

@@ -387,3 +387,12 @@ def test_v1_7_0_deprecate_gpu_stats_monitor(tmpdir):
 def test_v1_7_0_deprecate_xla_stats_monitor(tmpdir):
     with pytest.deprecated_call(match="The `XLAStatsMonitor` callback was deprecated in v1.5"):
         _ = XLAStatsMonitor()
+
+
+def test_v1_7_0_deprecated_max_steps_none(tmpdir):
+    with pytest.deprecated_call(match="`max_steps = None` is deprecated in v1.5"):
+        _ = Trainer(max_steps=None)
+
+    trainer = Trainer()
+    with pytest.deprecated_call(match="`max_steps = None` is deprecated in v1.5"):
+        trainer.fit_loop.max_steps = None

tests/trainer/flags/test_env_vars.py

@@ -21,10 +21,12 @@ def test_passing_no_env_variables():
     """Testing overwriting trainer arguments."""
     trainer = Trainer()
     assert trainer.logger is not None
-    assert trainer.max_steps is None
+    assert trainer.max_steps == -1
+    assert trainer.max_epochs == 1000
     trainer = Trainer(False, max_steps=42)
     assert trainer.logger is None
     assert trainer.max_steps == 42
+    assert trainer.max_epochs == -1
 
 
 @mock.patch.dict(os.environ, {"PL_TRAINER_LOGGER": "False", "PL_TRAINER_MAX_STEPS": "7"})

tests/trainer/optimization/test_optimizers.py

@@ -383,7 +383,7 @@ def test_lr_scheduler_strict(step_mock, tmpdir, complete_epoch):
     optimizer = optim.Adam(model.parameters())
     scheduler = optim.lr_scheduler.ReduceLROnPlateau(optimizer)
     max_epochs = 1 if complete_epoch else None
-    max_steps = None if complete_epoch else 1
+    max_steps = -1 if complete_epoch else 1
     trainer = Trainer(default_root_dir=tmpdir, max_epochs=max_epochs, max_steps=max_steps)
 
     model.configure_optimizers = lambda: {

tests/trainer/test_trainer.py

@@ -498,31 +498,30 @@ def test_trainer_max_steps_and_epochs(tmpdir):
 
 
 @pytest.mark.parametrize(
-    "max_epochs,max_steps,incorrect_variable,incorrect_value",
+    "max_epochs,max_steps,incorrect_variable",
     [
-        (-100, None, "max_epochs", -100),
-        (1, -2, "max_steps", -2),
+        (-100, -1, "max_epochs"),
+        (1, -2, "max_steps"),
     ],
 )
-def test_trainer_max_steps_and_epochs_validation(max_epochs, max_steps, incorrect_variable, incorrect_value):
+def test_trainer_max_steps_and_epochs_validation(max_epochs, max_steps, incorrect_variable):
     """Don't allow max_epochs or max_steps to be less than -1 or a float."""
     with pytest.raises(
         MisconfigurationException,
-        match=f"`{incorrect_variable}` must be a positive integer or -1. You passed in {incorrect_value}",
+        match=f"`{incorrect_variable}` must be a non-negative integer or -1",
     ):
         Trainer(max_epochs=max_epochs, max_steps=max_steps)
 
 
 @pytest.mark.parametrize(
     "max_epochs,max_steps,is_done,correct_trainer_epochs",
     [
-        (None, None, False, 1000),
-        (-1, None, False, -1),
-        (None, -1, False, None),
+        (None, -1, False, 1000),
+        (-1, -1, False, -1),
         (5, -1, False, 5),
         (-1, 10, False, -1),
-        (None, 0, True, None),
-        (0, None, True, 0),
+        (None, 0, True, -1),
+        (0, -1, True, 0),
         (-1, 0, True, -1),
         (0, -1, True, 0),
     ],

tests/trainer/test_trainer_cli.py

@@ -127,7 +127,6 @@ def _raise():
                 # These parameters are marked as Optional[...] in Trainer.__init__, with None as default.
                 # They should not be changed by the argparse interface.
                 "min_steps": None,
-                "max_steps": None,
                 "accelerator": None,
                 "weights_save_path": None,
                 "resume_from_checkpoint": None,

tests/utilities/test_cli.py

@@ -134,7 +134,6 @@ def _raise():
                 # with None as default. They should not be changed by the argparse
                 # interface.
                 min_steps=None,
-                max_steps=None,
                 accelerator=None,
                 weights_save_path=None,
                 resume_from_checkpoint=None,