lightning¶
Classes
The LightningModule - an nn.Module with many additional features.
- class pytorch_lightning.core.lightning.LightningModule(*args, **kwargs)[source]¶
Bases:
abc.ABC
,pytorch_lightning.core.mixins.device_dtype_mixin.DeviceDtypeModuleMixin
,pytorch_lightning.core.mixins.hparams_mixin.HyperparametersMixin
,pytorch_lightning.core.grads.GradInformation
,pytorch_lightning.core.saving.ModelIO
,pytorch_lightning.core.hooks.ModelHooks
,pytorch_lightning.core.hooks.DataHooks
,pytorch_lightning.core.hooks.CheckpointHooks
,torch.nn.modules.module.Module
- add_to_queue(queue)[source]¶
Appends the
trainer.callback_metrics
dictionary to the given queue. To avoid issues with memory sharing, we cast the data to numpy.
- all_gather(data, group=None, sync_grads=False)[source]¶
Allows users to call
self.all_gather()
from the LightningModule, thus making theall_gather
operation accelerator agnostic.all_gather
is a function provided by accelerators to gather a tensor from several distributed processes.- Parameters
data¶ (
Union
[Tensor
,Dict
,List
,Tuple
]) – int, float, tensor of shape (batch, …), or a (possibly nested) collection thereof.group¶ (
Optional
[Any
]) – the process group to gather results from. Defaults to all processes (world)sync_grads¶ (
bool
) – flag that allows users to synchronize gradients for the all_gather operation
- Returns
A tensor of shape (world_size, batch, …), or if the input was a collection the output will also be a collection with tensors of this shape.
- backward(loss, optimizer, optimizer_idx, *args, **kwargs)[source]¶
Called to perform backward on the loss returned in
training_step()
. Override this hook with your own implementation if you need to.- Parameters
loss¶ (
Tensor
) – The loss tensor returned bytraining_step()
. If gradient accumulation is used, the loss here holds the normalized value (scaled by 1 / accumulation steps).optimizer¶ (
Optional
[Optimizer
]) – Current optimizer being used.None
if using manual optimization.optimizer_idx¶ (
Optional
[int
]) – Index of the current optimizer being used.None
if using manual optimization.
- Return type
Example:
def backward(self, loss, optimizer, optimizer_idx): loss.backward()
- configure_callbacks()[source]¶
Configure model-specific callbacks. When the model gets attached, e.g., when
.fit()
or.test()
gets called, the list returned here will be merged with the list of callbacks passed to the Trainer’scallbacks
argument. If a callback returned here has the same type as one or several callbacks already present in the Trainer’s callbacks list, it will take priority and replace them. In addition, Lightning will make sureModelCheckpoint
callbacks run last.- Returns
A list of callbacks which will extend the list of callbacks in the Trainer.
Example:
def configure_callbacks(self): early_stop = EarlyStopping(monitor"val_acc", mode="max") checkpoint = ModelCheckpoint(monitor="val_loss") return [early_stop, checkpoint]
Note
Certain callback methods like
on_init_start()
will never be invoked on the new callbacks returned here.
- configure_optimizers()[source]¶
Choose what optimizers and learning-rate schedulers to use in your optimization. Normally you’d need one. But in the case of GANs or similar you might have multiple.
- Returns
Any of these 6 options.
Single optimizer.
List or Tuple of optimizers.
Two lists - The first list has multiple optimizers, and the second has multiple LR schedulers (or multiple
lr_dict
).Dictionary, with an
"optimizer"
key, and (optionally) a"lr_scheduler"
key whose value is a single LR scheduler orlr_dict
.Tuple of dictionaries as described above, with an optional
"frequency"
key.None - Fit will run without any optimizer.
The
lr_dict
is a dictionary which contains the scheduler and its associated configuration. The default configuration is shown below.lr_dict = { # REQUIRED: The scheduler instance "scheduler": lr_scheduler, # The unit of the scheduler's step size, could also be 'step'. # 'epoch' updates the scheduler on epoch end whereas 'step' # updates it after a optimizer update. "interval": "epoch", # How many epochs/steps should pass between calls to # `scheduler.step()`. 1 corresponds to updating the learning # rate after every epoch/step. "frequency": 1, # Metric to to monitor for schedulers like `ReduceLROnPlateau` "monitor": "val_loss", # If set to `True`, will enforce that the value specified 'monitor' # is available when the scheduler is updated, thus stopping # training if not found. If set to `False`, it will only produce a warning "strict": True, # If using the `LearningRateMonitor` callback to monitor the # learning rate progress, this keyword can be used to specify # a custom logged name "name": None, }
When there are schedulers in which the
.step()
method is conditioned on a value, such as thetorch.optim.lr_scheduler.ReduceLROnPlateau
scheduler, Lightning requires that thelr_dict
contains the keyword"monitor"
set to the metric name that the scheduler should be conditioned on.# The ReduceLROnPlateau scheduler requires a monitor def configure_optimizers(self): optimizer = Adam(...) return { "optimizer": optimizer, "lr_scheduler": { "scheduler": ReduceLROnPlateau(optimizer, ...), "monitor": "metric_to_track", }, } # In the case of two optimizers, only one using the ReduceLROnPlateau scheduler def configure_optimizers(self): optimizer1 = Adam(...) optimizer2 = SGD(...) scheduler1 = ReduceLROnPlateau(optimizer1, ...) scheduler2 = LambdaLR(optimizer2, ...) return ( { "optimizer": optimizer1, "lr_scheduler": { "scheduler": scheduler1, "monitor": "metric_to_track", }, }, {"optimizer": optimizer2, "lr_scheduler": scheduler2}, )
Metrics can be made available to monitor by simply logging it using
self.log('metric_to_track', metric_val)
in yourLightningModule
.Note
The
frequency
value specified in a dict along with theoptimizer
key is an int corresponding to the number of sequential batches optimized with the specific optimizer. It should be given to none or to all of the optimizers. There is a difference between passing multiple optimizers in a list, and passing multiple optimizers in dictionaries with a frequency of 1:In the former case, all optimizers will operate on the given batch in each optimization step.
In the latter, only one optimizer will operate on the given batch at every step.
This is different from the
frequency
value specified in thelr_dict
mentioned above.def configure_optimizers(self): optimizer_one = torch.optim.SGD(self.model.parameters(), lr=0.01) optimizer_two = torch.optim.SGD(self.model.parameters(), lr=0.01) return [ {"optimizer": optimizer_one, "frequency": 5}, {"optimizer": optimizer_two, "frequency": 10}, ]
In this example, the first optimizer will be used for the first 5 steps, the second optimizer for the next 10 steps and that cycle will continue. If an LR scheduler is specified for an optimizer using the
lr_scheduler
key in the above dict, the scheduler will only be updated when its optimizer is being used.Examples:
# most cases. no learning rate scheduler def configure_optimizers(self): return Adam(self.parameters(), lr=1e-3) # multiple optimizer case (e.g.: GAN) def configure_optimizers(self): gen_opt = Adam(self.model_gen.parameters(), lr=0.01) dis_opt = Adam(self.model_dis.parameters(), lr=0.02) return gen_opt, dis_opt # example with learning rate schedulers def configure_optimizers(self): gen_opt = Adam(self.model_gen.parameters(), lr=0.01) dis_opt = Adam(self.model_dis.parameters(), lr=0.02) dis_sch = CosineAnnealing(dis_opt, T_max=10) return [gen_opt, dis_opt], [dis_sch] # example with step-based learning rate schedulers # each optimizer has its own scheduler def configure_optimizers(self): gen_opt = Adam(self.model_gen.parameters(), lr=0.01) dis_opt = Adam(self.model_dis.parameters(), lr=0.02) gen_sch = { 'scheduler': ExponentialLR(gen_opt, 0.99), 'interval': 'step' # called after each training step } dis_sch = CosineAnnealing(dis_opt, T_max=10) # called every epoch return [gen_opt, dis_opt], [gen_sch, dis_sch] # example with optimizer frequencies # see training procedure in `Improved Training of Wasserstein GANs`, Algorithm 1 # https://arxiv.org/abs/1704.00028 def configure_optimizers(self): gen_opt = Adam(self.model_gen.parameters(), lr=0.01) dis_opt = Adam(self.model_dis.parameters(), lr=0.02) n_critic = 5 return ( {'optimizer': dis_opt, 'frequency': n_critic}, {'optimizer': gen_opt, 'frequency': 1} )
Note
Some things to know:
Lightning calls
.backward()
and.step()
on each optimizer and learning rate scheduler as needed.If you use 16-bit precision (
precision=16
), Lightning will automatically handle the optimizers.If you use multiple optimizers,
training_step()
will have an additionaloptimizer_idx
parameter.If you use
torch.optim.LBFGS
, Lightning handles the closure function automatically for you.If you use multiple optimizers, gradients will be calculated only for the parameters of current optimizer at each training step.
If you need to control how often those optimizers step or override the default
.step()
schedule, override theoptimizer_step()
hook.
- forward(*args, **kwargs)[source]¶
Same as
torch.nn.Module.forward()
.
- freeze()[source]¶
Freeze all params for inference.
Example:
model = MyLightningModule(...) model.freeze()
- Return type
- get_from_queue(queue)[source]¶
Retrieve the
trainer.callback_metrics
dictionary from the given queue. To preserve consistency, we cast back the data totorch.Tensor
.
- get_progress_bar_dict()[source]¶
Implement this to override the default items displayed in the progress bar. By default it includes the average loss value, split index of BPTT (if used) and the version of the experiment when using a logger.
Epoch 1: 4%|▎ | 40/1095 [00:03<01:37, 10.84it/s, loss=4.501, v_num=10]
Here is an example how to override the defaults:
def get_progress_bar_dict(self): # don't show the version number items = super().get_progress_bar_dict() items.pop("v_num", None) return items
- log(name, value, prog_bar=False, logger=True, on_step=None, on_epoch=None, reduce_fx='default', tbptt_reduce_fx=None, tbptt_pad_token=None, enable_graph=False, sync_dist=False, sync_dist_op=None, sync_dist_group=None, add_dataloader_idx=True, batch_size=None, metric_attribute=None, rank_zero_only=None)[source]¶
Log a key, value pair.
Example:
self.log('train_loss', loss)
The default behavior per hook is as follows:
*
also applies to the test loop¶LightningModule Hook
on_step
on_epoch
prog_bar
logger
training_step
T
F
F
T
training_step_end
T
F
F
T
training_epoch_end
F
T
F
T
validation_step*
F
T
F
T
validation_step_end*
F
T
F
T
validation_epoch_end*
F
T
F
T
- Parameters
name¶ – key to log
value¶ – value to log. Can be a
float
,Tensor
,Metric
, or a dictionary of the former.prog_bar¶ – if True logs to the progress bar
logger¶ – if True logs to the logger
on_step¶ – if True logs at this step. None auto-logs at the training_step but not validation/test_step
on_epoch¶ – if True logs epoch accumulated metrics. None auto-logs at the val/test step but not training_step
reduce_fx¶ – reduction function over step values for end of epoch.
torch.mean()
by default.enable_graph¶ – if True, will not auto detach the graph
sync_dist¶ – if True, reduces the metric across GPUs/TPUs
sync_dist_group¶ – the ddp group to sync across
add_dataloader_idx¶ – if True, appends the index of the current dataloader to the name (when using multiple). If False, user needs to give unique names for each dataloader to not mix values
batch_size¶ – Current batch_size. This will be directly inferred from the loaded batch, but some data structures might need to explicitly provide it.
metric_attribute¶ – To restore the metric state, Lightning requires the reference of the
torchmetrics.Metric
in your model. This is found automatically if it is a model attribute.rank_zero_only¶ – Whether the value will be logged only on rank 0. This will prevent synchronization which would produce a deadlock as not all processes would perform this log call.
- log_dict(dictionary, prog_bar=False, logger=True, on_step=None, on_epoch=None, reduce_fx='default', tbptt_reduce_fx=None, tbptt_pad_token=None, enable_graph=False, sync_dist=False, sync_dist_op=None, sync_dist_group=None, add_dataloader_idx=True)[source]¶
Log a dictionary of values at once.
Example:
values = {'loss': loss, 'acc': acc, ..., 'metric_n': metric_n} self.log_dict(values)
- Parameters
dictionary¶ (
Mapping
[str
,Union
[Metric
,Tensor
,Number
,Mapping
[str
,Union
[Metric
,Tensor
,Number
]]]]) – key value pairs. The values can be afloat
,Tensor
,Metric
, or a dictionary of the former.on_step¶ (
Optional
[bool
]) – if True logs at this step. None auto-logs for training_step but not validation/test_stepon_epoch¶ (
Optional
[bool
]) – if True logs epoch accumulated metrics. None auto-logs for val/test step but not training_stepreduce_fx¶ (
Union
[str
,Callable
]) – reduction function over step values for end of epoch.torch.mean()
by default.enable_graph¶ (
bool
) – if True, will not auto detach the graphsync_dist¶ (
bool
) – if True, reduces the metric across GPUs/TPUssync_dist_group¶ (
Optional
[Any
]) – the ddp group sync acrossadd_dataloader_idx¶ (
bool
) – if True, appends the index of the current dataloader to the name (when using multiple). If False, user needs to give unique names for each dataloader to not mix values
- Return type
- log_grad_norm(grad_norm_dict)[source]¶
Override this method to change the default behaviour of
log_grad_norm
.- Parameters
grad_norm_dict¶ (
Dict
[str
,Tensor
]) – Dictionary containing current grad norm metrics- Return type
Example:
# DEFAULT def log_grad_norm(self, grad_norm_dict): self.log_dict(grad_norm_dict, on_step=False, on_epoch=True, prog_bar=False, logger=True)
- lr_schedulers()[source]¶
Returns the learning rate scheduler(s) that are being used during training. Useful for manual optimization.
- manual_backward(loss, *args, **kwargs)[source]¶
Call this directly from your
training_step()
when doing optimizations manually. By using this, Lightning can ensure that all the proper scaling gets applied when using mixed precision.See manual optimization for more examples.
Example:
def training_step(...): opt = self.optimizers() loss = ... opt.zero_grad() # automatically applies scaling, etc... self.manual_backward(loss) opt.step()
- Parameters
loss¶ (
Tensor
) – The tensor on which to compute gradients. Must have a graph attached.*args¶ – Additional positional arguments to be forwarded to
backward()
**kwargs¶ – Additional keyword arguments to be forwarded to
backward()
- Return type
- optimizer_step(epoch=None, batch_idx=None, optimizer=None, optimizer_idx=None, optimizer_closure=None, on_tpu=None, using_native_amp=None, using_lbfgs=None)[source]¶
Override this method to adjust the default way the
Trainer
calls each optimizer. By default, Lightning callsstep()
andzero_grad()
as shown in the example once per optimizer. This method (andzero_grad()
) won’t be called during the accumulation phase whenTrainer(accumulate_grad_batches != 1)
.Warning
If you are overriding this method, make sure that you pass the
optimizer_closure
parameter tooptimizer.step()
function as shown in the examples. This ensures thattraining_step()
,optimizer.zero_grad()
,backward()
are called within the training loop.- Parameters
optimizer_idx¶ (
Optional
[int
]) – If you used multiple optimizers, this indexes into that list.optimizer_closure¶ (
Optional
[Callable
]) – Closure for all optimizersusing_native_amp¶ (
Optional
[bool
]) –True
if using native ampusing_lbfgs¶ (
Optional
[bool
]) – True if the matching optimizer istorch.optim.LBFGS
- Return type
Examples:
# DEFAULT def optimizer_step(self, epoch, batch_idx, optimizer, optimizer_idx, optimizer_closure, on_tpu, using_native_amp, using_lbfgs): optimizer.step(closure=optimizer_closure) # Alternating schedule for optimizer steps (i.e.: GANs) def optimizer_step(self, epoch, batch_idx, optimizer, optimizer_idx, optimizer_closure, on_tpu, using_native_amp, using_lbfgs): # update generator opt every step if optimizer_idx == 0: optimizer.step(closure=optimizer_closure) # update discriminator opt every 2 steps if optimizer_idx == 1: if (batch_idx + 1) % 2 == 0 : optimizer.step(closure=optimizer_closure) # ... # add as many optimizers as you want
Here’s another example showing how to use this for more advanced things such as learning rate warm-up:
# learning rate warm-up def optimizer_step( self, epoch, batch_idx, optimizer, optimizer_idx, optimizer_closure, on_tpu, using_native_amp, using_lbfgs, ): # warm up lr if self.trainer.global_step < 500: lr_scale = min(1.0, float(self.trainer.global_step + 1) / 500.0) for pg in optimizer.param_groups: pg["lr"] = lr_scale * self.learning_rate # update params optimizer.step(closure=optimizer_closure)
- optimizer_zero_grad(epoch, batch_idx, optimizer, optimizer_idx)[source]¶
Override this method to change the default behaviour of
optimizer.zero_grad()
.- Parameters
Examples:
# DEFAULT def optimizer_zero_grad(self, epoch, batch_idx, optimizer, optimizer_idx): optimizer.zero_grad() # Set gradients to `None` instead of zero to improve performance. def optimizer_zero_grad(self, epoch, batch_idx, optimizer, optimizer_idx): optimizer.zero_grad(set_to_none=True)
See
torch.optim.Optimizer.zero_grad()
for the explanation of the above example.
- optimizers(use_pl_optimizer=True)[source]¶
Returns the optimizer(s) that are being used during training. Useful for manual optimization.
- Parameters
use_pl_optimizer¶ (
bool
) – IfTrue
, will wrap the optimizer(s) in aLightningOptimizer
for automatic handling of precision and profiling.- Return type
Union
[Optimizer
,LightningOptimizer
,List
[Optimizer
],List
[LightningOptimizer
]]- Returns
A single optimizer, or a list of optimizers in case multiple ones are present.
- predict_step(batch, batch_idx, dataloader_idx=None)[source]¶
Step function called during
predict()
. By default, it callsforward()
. Override to add any processing logic.The
predict_step()
is used to scale inference on multi-devices.To prevent an OOM error, it is possible to use
BasePredictionWriter
callback to write the predictions to disk or database after each batch or on epoch end.The
BasePredictionWriter
should be used while using a spawn based accelerator. This happens forTrainer(accelerator="ddp_spawn")
or training on 8 TPU cores withTrainer(tpu_cores=8)
as predictions won’t be returned.Example
class MyModel(LightningModule): def predicts_step(self, batch, batch_idx, dataloader_idx): return self(batch) dm = ... model = MyModel() trainer = Trainer(gpus=2) predictions = trainer.predict(model, dm)
- print(*args, **kwargs)[source]¶
Prints only from process 0. Use this in any distributed mode to log only once.
- Parameters
- Return type
Example:
def forward(self, x): self.print(x, 'in forward')
- summarize(mode='top', max_depth=None)[source]¶
Summarize this LightningModule.
- Parameters
Can be either
'top'
(summarize only direct submodules) or'full'
(summarize all layers).Deprecated since version v1.4: This parameter was deprecated in v1.4 in favor of max_depth and will be removed in v1.6.
max_depth¶ (
Optional
[int
]) – The maximum depth of layer nesting that the summary will include. A value of 0 turns the layer summary off. Default: 1.
- Return type
Optional
[ModelSummary
]- Returns
The model summary object
- tbptt_split_batch(batch, split_size)[source]¶
When using truncated backpropagation through time, each batch must be split along the time dimension. Lightning handles this by default, but for custom behavior override this function.
- Parameters
- Return type
- Returns
List of batch splits. Each split will be passed to
training_step()
to enable truncated back propagation through time. The default implementation splits root level Tensors and Sequences at dim=1 (i.e. time dim). It assumes that each time dim is the same length.
Examples:
def tbptt_split_batch(self, batch, split_size): splits = [] for t in range(0, time_dims[0], split_size): batch_split = [] for i, x in enumerate(batch): if isinstance(x, torch.Tensor): split_x = x[:, t:t + split_size] elif isinstance(x, collections.Sequence): split_x = [None] * len(x) for batch_idx in range(len(x)): split_x[batch_idx] = x[batch_idx][t:t + split_size] batch_split.append(split_x) splits.append(batch_split) return splits
Note
Called in the training loop after
on_batch_start()
iftruncated_bptt_steps
> 0. Each returned batch split is passed separately totraining_step()
.
- test_epoch_end(outputs)[source]¶
Called at the end of a test epoch with the output of all test steps.
# the pseudocode for these calls test_outs = [] for test_batch in test_data: out = test_step(test_batch) test_outs.append(out) test_epoch_end(test_outs)
- Parameters
outputs¶ (
List
[Union
[Tensor
,Dict
[str
,Any
]]]) – List of outputs you defined intest_step_end()
, or if there are multiple dataloaders, a list containing a list of outputs for each dataloader- Return type
- Returns
None
Note
If you didn’t define a
test_step()
, this won’t be called.Examples
With a single dataloader:
def test_epoch_end(self, outputs): # do something with the outputs of all test batches all_test_preds = test_step_outputs.predictions some_result = calc_all_results(all_test_preds) self.log(some_result)
With multiple dataloaders, outputs will be a list of lists. The outer list contains one entry per dataloader, while the inner list contains the individual outputs of each test step for that dataloader.
def test_epoch_end(self, outputs): final_value = 0 for dataloader_outputs in outputs: for test_step_out in dataloader_outputs: # do something final_value += test_step_out self.log("final_metric", final_value)
- test_step(*args, **kwargs)[source]¶
Operates on a single batch of data from the test set. In this step you’d normally generate examples or calculate anything of interest such as accuracy.
# the pseudocode for these calls test_outs = [] for test_batch in test_data: out = test_step(test_batch) test_outs.append(out) test_epoch_end(test_outs)
- Parameters
- Return type
- Returns
Any of.
Any object or value
None
- Testing will skip to the next batch
# if you have one test dataloader: def test_step(self, batch, batch_idx): ... # if you have multiple test dataloaders: def test_step(self, batch, batch_idx, dataloader_idx): ...
Examples:
# CASE 1: A single test dataset def test_step(self, batch, batch_idx): x, y = batch # implement your own out = self(x) loss = self.loss(out, y) # log 6 example images # or generated text... or whatever sample_imgs = x[:6] grid = torchvision.utils.make_grid(sample_imgs) self.logger.experiment.add_image('example_images', grid, 0) # calculate acc labels_hat = torch.argmax(out, dim=1) test_acc = torch.sum(y == labels_hat).item() / (len(y) * 1.0) # log the outputs! self.log_dict({'test_loss': loss, 'test_acc': test_acc})
If you pass in multiple test dataloaders,
test_step()
will have an additional argument.# CASE 2: multiple test dataloaders def test_step(self, batch, batch_idx, dataloader_idx): # dataloader_idx tells you which dataset this is. ...
Note
If you don’t need to test you don’t need to implement this method.
Note
When the
test_step()
is called, the model has been put in eval mode and PyTorch gradients have been disabled. At the end of the test epoch, the model goes back to training mode and gradients are enabled.
- test_step_end(*args, **kwargs)[source]¶
Use this when testing with dp or ddp2 because
test_step()
will operate on only part of the batch. However, this is still optional and only needed for things like softmax or NCE loss.Note
If you later switch to ddp or some other mode, this will still be called so that you don’t have to change your code.
# pseudocode sub_batches = split_batches_for_dp(batch) batch_parts_outputs = [test_step(sub_batch) for sub_batch in sub_batches] test_step_end(batch_parts_outputs)
- Parameters
batch_parts_outputs¶ – What you return in
test_step()
for each batch part.- Return type
- Returns
None or anything
# WITHOUT test_step_end # if used in DP or DDP2, this batch is 1/num_gpus large def test_step(self, batch, batch_idx): # batch is 1/num_gpus big x, y = batch out = self(x) loss = self.softmax(out) self.log("test_loss", loss) # -------------- # with test_step_end to do softmax over the full batch def test_step(self, batch, batch_idx): # batch is 1/num_gpus big x, y = batch out = self.encoder(x) return out def test_step_end(self, output_results): # this out is now the full size of the batch all_test_step_outs = output_results.out loss = nce_loss(all_test_step_outs) self.log("test_loss", loss)
See also
See the Multi-GPU training guide for more details.
- to_onnx(file_path, input_sample=None, **kwargs)[source]¶
Saves the model in ONNX format.
- Parameters
Example
>>> class SimpleModel(LightningModule): ... def __init__(self): ... super().__init__() ... self.l1 = torch.nn.Linear(in_features=64, out_features=4) ... ... def forward(self, x): ... return torch.relu(self.l1(x.view(x.size(0), -1)))
>>> with tempfile.NamedTemporaryFile(suffix='.onnx', delete=False) as tmpfile: ... model = SimpleModel() ... input_sample = torch.randn((1, 64)) ... model.to_onnx(tmpfile.name, input_sample, export_params=True) ... os.path.isfile(tmpfile.name) True
- to_torchscript(file_path=None, method='script', example_inputs=None, **kwargs)[source]¶
By default compiles the whole model to a
ScriptModule
. If you want to use tracing, please provided the argumentmethod='trace'
and make sure that either the example_inputs argument is provided, or the model hasexample_input_array
set. If you would like to customize the modules that are scripted you should override this method. In case you want to return multiple modules, we recommend using a dictionary.- Parameters
file_path¶ (
Union
[str
,Path
,None
]) – Path where to save the torchscript. Default: None (no file saved).method¶ (
Optional
[str
]) – Whether to use TorchScript’s script or trace method. Default: ‘script’example_inputs¶ (
Optional
[Any
]) – An input to be used to do tracing when method is set to ‘trace’. Default: None (usesexample_input_array
)**kwargs¶ – Additional arguments that will be passed to the
torch.jit.script()
ortorch.jit.trace()
function.
Note
Example
>>> class SimpleModel(LightningModule): ... def __init__(self): ... super().__init__() ... self.l1 = torch.nn.Linear(in_features=64, out_features=4) ... ... def forward(self, x): ... return torch.relu(self.l1(x.view(x.size(0), -1))) ... >>> model = SimpleModel() >>> torch.jit.save(model.to_torchscript(), "model.pt") >>> os.path.isfile("model.pt") >>> torch.jit.save(model.to_torchscript(file_path="model_trace.pt", method='trace', ... example_inputs=torch.randn(1, 64))) >>> os.path.isfile("model_trace.pt") True
- toggle_optimizer(optimizer, optimizer_idx)[source]¶
Makes sure only the gradients of the current optimizer’s parameters are calculated in the training step to prevent dangling gradients in multiple-optimizer setup. It works with
untoggle_optimizer()
to make sureparam_requires_grad_state
is properly reset. Override for your own behavior.- Parameters
Note
Only called when using multiple optimizers
- training_epoch_end(outputs)[source]¶
Called at the end of the training epoch with the outputs of all training steps. Use this in case you need to do something with all the outputs returned by
training_step()
.# the pseudocode for these calls train_outs = [] for train_batch in train_data: out = training_step(train_batch) train_outs.append(out) training_epoch_end(train_outs)
- Parameters
outputs¶ (
List
[Union
[Tensor
,Dict
[str
,Any
]]]) – List of outputs you defined intraining_step()
, or if there are multiple dataloaders, a list containing a list of outputs for each dataloader.- Return type
- Returns
None
Note
If this method is not overridden, this won’t be called.
Example:
def training_epoch_end(self, training_step_outputs): # do something with all training_step outputs return result
With multiple dataloaders,
outputs
will be a list of lists. The outer list contains one entry per dataloader, while the inner list contains the individual outputs of each training step for that dataloader.def training_epoch_end(self, training_step_outputs): for out in training_step_outputs: ...
- training_step(*args, **kwargs)[source]¶
Here you compute and return the training loss and some additional metrics for e.g. the progress bar or logger.
- Parameters
batch¶ (
Tensor
| (Tensor
, …) | [Tensor
, …]) – The output of yourDataLoader
. A tensor, tuple or list.optimizer_idx¶ (int) – When using multiple optimizers, this argument will also be present.
hiddens¶ (
Tensor
) – Passed in iftruncated_bptt_steps
> 0.
- Return type
- Returns
Any of.
Tensor
- The loss tensordict
- A dictionary. Can include any keys, but must include the key'loss'
None
- Training will skip to the next batch
Note
Returning
None
is currently not supported for multi-GPU or TPU, or with 16-bit precision enabled.In this step you’d normally do the forward pass and calculate the loss for a batch. You can also do fancier things like multiple forward passes or something model specific.
Example:
def training_step(self, batch, batch_idx): x, y, z = batch out = self.encoder(x) loss = self.loss(out, x) return loss
If you define multiple optimizers, this step will be called with an additional
optimizer_idx
parameter.# Multiple optimizers (e.g.: GANs) def training_step(self, batch, batch_idx, optimizer_idx): if optimizer_idx == 0: # do training_step with encoder ... if optimizer_idx == 1: # do training_step with decoder ...
If you add truncated back propagation through time you will also get an additional argument with the hidden states of the previous step.
# Truncated back-propagation through time def training_step(self, batch, batch_idx, hiddens): # hiddens are the hidden states from the previous truncated backprop step ... out, hiddens = self.lstm(data, hiddens) ... return {"loss": loss, "hiddens": hiddens}
Note
The loss value shown in the progress bar is smoothed (averaged) over the last values, so it differs from the actual loss returned in train/validation step.
- training_step_end(*args, **kwargs)[source]¶
Use this when training with dp or ddp2 because
training_step()
will operate on only part of the batch. However, this is still optional and only needed for things like softmax or NCE loss.Note
If you later switch to ddp or some other mode, this will still be called so that you don’t have to change your code
# pseudocode sub_batches = split_batches_for_dp(batch) batch_parts_outputs = [training_step(sub_batch) for sub_batch in sub_batches] training_step_end(batch_parts_outputs)
- Parameters
batch_parts_outputs¶ – What you return in training_step for each batch part.
- Return type
- Returns
Anything
When using dp/ddp2 distributed backends, only a portion of the batch is inside the training_step:
def training_step(self, batch, batch_idx): # batch is 1/num_gpus big x, y = batch out = self(x) # softmax uses only a portion of the batch in the denominator loss = self.softmax(out) loss = nce_loss(loss) return loss
If you wish to do something with all the parts of the batch, then use this method to do it:
def training_step(self, batch, batch_idx): # batch is 1/num_gpus big x, y = batch out = self.encoder(x) return {"pred": out} def training_step_end(self, training_step_outputs): gpu_0_pred = training_step_outputs[0]["pred"] gpu_1_pred = training_step_outputs[1]["pred"] gpu_n_pred = training_step_outputs[n]["pred"] # this softmax now uses the full batch loss = nce_loss([gpu_0_pred, gpu_1_pred, gpu_n_pred]) return loss
See also
See the Multi-GPU training guide for more details.
- unfreeze()[source]¶
Unfreeze all parameters for training.
model = MyLightningModule(...) model.unfreeze()
- Return type
- untoggle_optimizer(optimizer_idx)[source]¶
Resets the state of required gradients that were toggled with
toggle_optimizer()
. Override for your own behavior.Note
Only called when using multiple optimizers
- validation_epoch_end(outputs)[source]¶
Called at the end of the validation epoch with the outputs of all validation steps.
# the pseudocode for these calls val_outs = [] for val_batch in val_data: out = validation_step(val_batch) val_outs.append(out) validation_epoch_end(val_outs)
- Parameters
outputs¶ (
List
[Union
[Tensor
,Dict
[str
,Any
]]]) – List of outputs you defined invalidation_step()
, or if there are multiple dataloaders, a list containing a list of outputs for each dataloader.- Return type
- Returns
None
Note
If you didn’t define a
validation_step()
, this won’t be called.Examples
With a single dataloader:
def validation_epoch_end(self, val_step_outputs): for out in val_step_outputs: ...
With multiple dataloaders, outputs will be a list of lists. The outer list contains one entry per dataloader, while the inner list contains the individual outputs of each validation step for that dataloader.
def validation_epoch_end(self, outputs): for dataloader_output_result in outputs: dataloader_outs = dataloader_output_result.dataloader_i_outputs self.log("final_metric", final_value)
- validation_step(*args, **kwargs)[source]¶
Operates on a single batch of data from the validation set. In this step you’d might generate examples or calculate anything of interest like accuracy.
# the pseudocode for these calls val_outs = [] for val_batch in val_data: out = validation_step(val_batch) val_outs.append(out) validation_epoch_end(val_outs)
- Parameters
- Return type
- Returns
Any object or value
None
- Validation will skip to the next batch
# pseudocode of order val_outs = [] for val_batch in val_data: out = validation_step(val_batch) if defined("validation_step_end"): out = validation_step_end(out) val_outs.append(out) val_outs = validation_epoch_end(val_outs)
# if you have one val dataloader: def validation_step(self, batch, batch_idx): ... # if you have multiple val dataloaders: def validation_step(self, batch, batch_idx, dataloader_idx): ...
Examples:
# CASE 1: A single validation dataset def validation_step(self, batch, batch_idx): x, y = batch # implement your own out = self(x) loss = self.loss(out, y) # log 6 example images # or generated text... or whatever sample_imgs = x[:6] grid = torchvision.utils.make_grid(sample_imgs) self.logger.experiment.add_image('example_images', grid, 0) # calculate acc labels_hat = torch.argmax(out, dim=1) val_acc = torch.sum(y == labels_hat).item() / (len(y) * 1.0) # log the outputs! self.log_dict({'val_loss': loss, 'val_acc': val_acc})
If you pass in multiple val dataloaders,
validation_step()
will have an additional argument.# CASE 2: multiple validation dataloaders def validation_step(self, batch, batch_idx, dataloader_idx): # dataloader_idx tells you which dataset this is. ...
Note
If you don’t need to validate you don’t need to implement this method.
Note
When the
validation_step()
is called, the model has been put in eval mode and PyTorch gradients have been disabled. At the end of validation, the model goes back to training mode and gradients are enabled.
- validation_step_end(*args, **kwargs)[source]¶
Use this when validating with dp or ddp2 because
validation_step()
will operate on only part of the batch. However, this is still optional and only needed for things like softmax or NCE loss.Note
If you later switch to ddp or some other mode, this will still be called so that you don’t have to change your code.
# pseudocode sub_batches = split_batches_for_dp(batch) batch_parts_outputs = [validation_step(sub_batch) for sub_batch in sub_batches] validation_step_end(batch_parts_outputs)
- Parameters
batch_parts_outputs¶ – What you return in
validation_step()
for each batch part.- Return type
- Returns
None or anything
# WITHOUT validation_step_end # if used in DP or DDP2, this batch is 1/num_gpus large def validation_step(self, batch, batch_idx): # batch is 1/num_gpus big x, y = batch out = self.encoder(x) loss = self.softmax(out) loss = nce_loss(loss) self.log("val_loss", loss) # -------------- # with validation_step_end to do softmax over the full batch def validation_step(self, batch, batch_idx): # batch is 1/num_gpus big x, y = batch out = self(x) return out def validation_step_end(self, val_step_outputs): for out in val_step_outputs: ...
See also
See the Multi-GPU training guide for more details.
- write_prediction(name, value, filename='predictions.pt')[source]¶
Write predictions to disk using
torch.save
Example:
self.write_prediction('pred', torch.tensor(...), filename='my_predictions.pt')
- Parameters
Note
when running in distributed mode, calling
write_prediction
will create a file for each device with respective names:filename_rank_0.pt
,filename_rank_1.pt
, …
- write_prediction_dict(predictions_dict, filename='predictions.pt')[source]¶
Write a dictonary of predictions to disk at once using
torch.save
Example:
pred_dict = {'pred1': torch.tensor(...), 'pred2': torch.tensor(...)} self.write_prediction_dict(pred_dict)
- Parameters
predictions_dict¶ (
Dict
[str
,Any
]) – dict containing predictions, where each prediction should either be singleTensor
or a list of them
Note
when running in distributed mode, calling
write_prediction_dict
will create a file for each device with respective names:filename_rank_0.pt
,filename_rank_1.pt
, …
- property automatic_optimization: bool¶
If set to
False
you are responsible for calling.backward()
,.step()
,.zero_grad()
.
- property current_epoch: int¶
The current epoch in the Trainer. If no Trainer is attached, this propery is 0.
- property example_input_array: Any¶
The example input array is a specification of what the module can consume in the
forward()
method. The return type is interpreted as follows:Single tensor: It is assumed the model takes a single argument, i.e.,
model.forward(model.example_input_array)
Tuple: The input array should be interpreted as a sequence of positional arguments, i.e.,
model.forward(*model.example_input_array)
Dict: The input array represents named keyword arguments, i.e.,
model.forward(**model.example_input_array)
- property global_rank: int¶
The index of the current process across all nodes and devices.
- property global_step: int¶
Total training batches seen across all epochs. If no Trainer is attached, this propery is 0.
- property local_rank: int¶
The index of the current process within a single node.
- property logger¶
Reference to the logger object in the Trainer.
- property model_size: float¶
The model’s size in megabytes. The computation includes everything in the
state_dict()
, i.e., by default the parameteters and buffers.
- property on_gpu¶
Returns
True
if this model is currently located on a GPU. Useful to set flags around the LightningModule for different CPU vs GPU behavior.
- property truncated_bptt_steps: int¶
Enables Truncated Backpropagation Through Time in the Trainer when set to a positive integer. It represents the number of times
training_step()
gets called before backpropagation. If this is > 0, thetraining_step()
receives an additional argumenthiddens
and is expected to return a hidden state.