SDK ML Classification API
This module contains functions to compute and display classification KPIs
-
metavision_ml.classification.utils_metrics.
calculate_time_to_prediction
(pred_seq, label_seq, delta_t=10000) calculate KPI: time to 1st correct prediction & draw histogram of the time to prediction statistics
- Parameters
pred_seq (list) – list of prediction tensors for each data sample
labels_all (list) – list of label tensors for each data sample
delta_t (int) – time interval of data sample
-
metavision_ml.classification.utils_metrics.
evaluate_preds_seq
(preds_seq, labels_seq, res_per_recording, hparams, latency_seq) Inspect the test result by plotting the recording image together with prediction sequence
- Parameters
preds_seq (list) – nested list of prediction sequences
labels_seq (list) – nested list of labeling sequences
res_per_recording (defaultdict) – defaultdict of time stamp, prediction and label vectors per HDF5 file
hparams (dict) – hyperparameters
latency_seq – list of time to prediction for each data sample
-
metavision_ml.classification.utils_metrics.
get_1st_nonzeros
(tensor) Get the 1st nonzero item along the last axis of the tensor If tensor only contains zeros, get the last item index :param tensor: input tensor :type tensor: torch.Tensor
-
metavision_ml.classification.utils_metrics.
plot_cm
(preds_all, labels_all, labels) Plot confusion metrics & error map by masking the diagonal values
- Parameters
preds_all (torch.Tensor) – predictions
labels_all (torch.Tensor) – GT
labels (list) – list of all class labels
-
metavision_ml.classification.utils_metrics.
plot_precision_recall_curve
(preds_all, labels_all, labels) plot the PR-curve
- Parameters
preds_all (torch.Tensor) – predictions
labels_all (torch.Tensor) – GT
labels (list) – list of all class labels
-
metavision_ml.classification.utils_metrics.
plot_roc
(preds_all, labels_all, labels) plot roc curve with auc_roc score
- Parameters
preds_all (torch.Tensor) – predictions
labels_all (torch.Tensor) – GT
labels (list) – list of all class labels
-
metavision_ml.classification.utils_metrics.
unpack_metrics_dict
(metrics_per_category, label) Unpack the dense metrics
- Parameters
metrics_per_category (dict) – the torchmetrics result calculated per category
label (list) – list of class labels
This data module is a wrapper around SequentialDataLoader for the classification module.
-
class
metavision_ml.classification.data_module.
ClassificationDataModule
(hparams, data_dir: str = '') Data Module for classification Applies some data augmentation on top.
Attributes: prepare_data_per_node:
If True, each LOCAL_RANK=0 will call prepare data. Otherwise only NODE_RANK=0, LOCAL_RANK=0 will prepare data.
- allow_zero_length_dataloader_with_multiple_devices:
If True, dataloader with zero length within local rank is allowed. Default value is False.
-
test_dataloader
() Implement one or multiple PyTorch DataLoaders for testing.
For data processing use the following pattern:
download in
prepare_data()
process and split in
setup()
However, the above are only necessary for distributed processing.
Warning
do not assign state in prepare_data
test()
prepare_data()
setup()
Note
Lightning adds the correct sampler for distributed and arbitrary hardware. There is no need to set it yourself.
- Returns
A
torch.utils.data.DataLoader
or a sequence of them specifying testing samples.
Example:
def test_dataloader(self): transform = transforms.Compose([transforms.ToTensor(), transforms.Normalize((0.5,), (1.0,))]) dataset = MNIST(root='/path/to/mnist/', train=False, transform=transform, download=True) loader = torch.utils.data.DataLoader( dataset=dataset, batch_size=self.batch_size, shuffle=False ) return loader # can also return multiple dataloaders def test_dataloader(self): return [loader_a, loader_b, ..., loader_n]
Note
If you don’t need a test dataset and a
test_step()
, you don’t need to implement this method.Note
In the case where you return multiple test dataloaders, the
test_step()
will have an argumentdataloader_idx
which matches the order here.
-
train_dataloader
() Implement one or more PyTorch DataLoaders for training.
- Returns
A collection of
torch.utils.data.DataLoader
specifying training samples. In the case of multiple dataloaders, please see this section.
The dataloader you return will not be reloaded unless you set :paramref:`~pytorch_lightning.trainer.Trainer.reload_dataloaders_every_n_epochs` to a positive integer.
For data processing use the following pattern:
download in
prepare_data()
process and split in
setup()
However, the above are only necessary for distributed processing.
Warning
do not assign state in prepare_data
fit()
prepare_data()
setup()
Note
Lightning adds the correct sampler for distributed and arbitrary hardware. There is no need to set it yourself.
Example:
# single dataloader def train_dataloader(self): transform = transforms.Compose([transforms.ToTensor(), transforms.Normalize((0.5,), (1.0,))]) dataset = MNIST(root='/path/to/mnist/', train=True, transform=transform, download=True) loader = torch.utils.data.DataLoader( dataset=dataset, batch_size=self.batch_size, shuffle=True ) return loader # multiple dataloaders, return as list def train_dataloader(self): mnist = MNIST(...) cifar = CIFAR(...) mnist_loader = torch.utils.data.DataLoader( dataset=mnist, batch_size=self.batch_size, shuffle=True ) cifar_loader = torch.utils.data.DataLoader( dataset=cifar, batch_size=self.batch_size, shuffle=True ) # each batch will be a list of tensors: [batch_mnist, batch_cifar] return [mnist_loader, cifar_loader] # multiple dataloader, return as dict def train_dataloader(self): mnist = MNIST(...) cifar = CIFAR(...) mnist_loader = torch.utils.data.DataLoader( dataset=mnist, batch_size=self.batch_size, shuffle=True ) cifar_loader = torch.utils.data.DataLoader( dataset=cifar, batch_size=self.batch_size, shuffle=True ) # each batch will be a dict of tensors: {'mnist': batch_mnist, 'cifar': batch_cifar} return {'mnist': mnist_loader, 'cifar': cifar_loader}
-
transfer_batch_to_device
(batch, device, dataloader_idx) Override this hook if your
DataLoader
returns tensors wrapped in a custom data structure.The data types listed below (and any arbitrary nesting of them) are supported out of the box:
torch.Tensor
or anything that implements .to(…)list
dict
tuple
For anything else, you need to define how the data is moved to the target device (CPU, GPU, TPU, …).
Note
This hook should only transfer the data and not modify it, nor should it move the data to any other device than the one passed in as argument (unless you know what you are doing). To check the current state of execution of this hook you can use
self.trainer.training/testing/validating/predicting
so that you can add different logic as per your requirement.Note
This hook only runs on single GPU training and DDP (no data-parallel). Data-Parallel support will come in near future.
- Parameters
batch – A batch of data that needs to be transferred to a new device.
device – The target device as defined in PyTorch.
dataloader_idx – The index of the dataloader to which the batch belongs.
- Returns
A reference to the data on the new device.
Example:
def transfer_batch_to_device(self, batch, device, dataloader_idx): if isinstance(batch, CustomBatch): # move all tensors in your custom data structure to the device batch.samples = batch.samples.to(device) batch.targets = batch.targets.to(device) elif dataloader_idx == 0: # skip device transfer for the first dataloader or anything you wish pass else: batch = super().transfer_batch_to_device(data, device, dataloader_idx) return batch
- Raises
MisconfigurationException – If using data-parallel,
Trainer(strategy='dp')
.MisconfigurationException – If using IPUs,
Trainer(accelerator='ipu')
.
See also
move_data_to_device()
apply_to_collection()
-
val_dataloader
() Implement one or multiple PyTorch DataLoaders for validation.
The dataloader you return will not be reloaded unless you set :paramref:`~pytorch_lightning.trainer.Trainer.reload_dataloaders_every_n_epochs` to a positive integer.
It’s recommended that all data downloads and preparation happen in
prepare_data()
.fit()
validate()
prepare_data()
setup()
Note
Lightning adds the correct sampler for distributed and arbitrary hardware There is no need to set it yourself.
- Returns
A
torch.utils.data.DataLoader
or a sequence of them specifying validation samples.
Examples:
def val_dataloader(self): transform = transforms.Compose([transforms.ToTensor(), transforms.Normalize((0.5,), (1.0,))]) dataset = MNIST(root='/path/to/mnist/', train=False, transform=transform, download=True) loader = torch.utils.data.DataLoader( dataset=dataset, batch_size=self.batch_size, shuffle=False ) return loader # can also return multiple dataloaders def val_dataloader(self): return [loader_a, loader_b, ..., loader_n]
Note
If you don’t need a validation dataset and a
validation_step()
, you don’t need to implement this method.Note
In the case where you return multiple validation dataloaders, the
validation_step()
will have an argumentdataloader_idx
which matches the order here.
-
metavision_ml.classification.data_module.
load_classes
(metadata, batch_start_time, duration, tensor, **kwargs) Function to fetch boxes and preprocess them. Should be passed to a SequentialDataLoader.
Examples
>>> from functools import partial >>> n_classes = 21 >>> class_lookup = np.arange(n_classes) # each class is mapped to itself >>> load_boxes_function = partial(load_boxes, class_lookup=class_lookup)
- Parameters
metadata (object) – Record details.
batch_start_time (int) – (us) Where to seek in the file to load corresponding bounding boxes
duration (int) – (us) How long to load events from bounding box file
tensor (np.ndarray) – Current preprocessed input, can be used for data dependent preprocessing, for instance remove boxes without any features in them.
class_lookup (np.array) – Look up array for class indices.
labelling_delta_t (int) – Indicates the period of labelling in order to only consider time bins with actual labels when computing the loss.
- Returns
List of structured array of dtype EventBbox corresponding to each time bins. frame_is_labeled (np.ndarray): This boolean mask array of length num_tbins indicates whether the frame contains a label. It is used to differentiate between time bins that actually contain an empty label (for instance no bounding boxes) from time bins that weren’t labeled due to cost constraints. The latter time bins shouldn’t contribute to supervised losses used during training.
- Return type
labels (List[np.ndarray])
Models for classification
-
class
metavision_ml.classification.models.
ConvRNNClassifier
(cin=1, base=16, cout=256, num_classes=2) ConvRNN Classifier
Feed-Forward + RNN light model
- Parameters
cin (int) – aaa
base (int) – bbb
cout (int) – ccc
num_classes (int) – ddd
Initializes internal Module state, shared by both nn.Module and ScriptModule.
-
forward
(x) Defines the computation performed at every call.
Should be overridden by all subclasses.
Note
Although the recipe for forward pass needs to be defined within this function, one should call the
Module
instance afterwards instead of this since the former takes care of running the registered hooks while the latter silently ignores them.
-
class
metavision_ml.classification.models.
LeNetClassifier
(cin=1, base=6, cout=256, num_classes=2) LeNet RNN
Initializes internal Module state, shared by both nn.Module and ScriptModule.
-
forward
(x) Defines the computation performed at every call.
Should be overridden by all subclasses.
Note
Although the recipe for forward pass needs to be defined within this function, one should call the
Module
instance afterwards instead of this since the former takes care of running the registered hooks while the latter silently ignores them.
-
-
class
metavision_ml.classification.models.
Mobilenetv2Classifier
(cin=2, width_mul=1.0, num_classes=2, round_nearest=8, **kwargs) Mobilenetv2
Modified Feed-Forward architecture
Initializes internal Module state, shared by both nn.Module and ScriptModule.
-
forward
(x) Defines the computation performed at every call.
Should be overridden by all subclasses.
Note
Although the recipe for forward pass needs to be defined within this function, one should call the
Module
instance afterwards instead of this since the former takes care of running the registered hooks while the latter silently ignores them.
-
-
class
metavision_ml.classification.models.
SqueezenetClassifier
(cin=2, num_classes=2, **kwargs) Mobilenetv2
Modified Feed-Forward architecture
Initializes internal Module state, shared by both nn.Module and ScriptModule.
-
forward
(x) Defines the computation performed at every call.
Should be overridden by all subclasses.
Note
Although the recipe for forward pass needs to be defined within this function, one should call the
Module
instance afterwards instead of this since the former takes care of running the registered hooks while the latter silently ignores them.
-
Pytorch Lightning Module for training a classifier
-
class
metavision_ml.classification.lightning_model.
ClassificationModel
(hparams: argparse.Namespace) Pytorch Lightning model for neural network to predict class of scene.
- Parameters
hparams (argparse.Namespace) – argparse from train.py application
-
configure_optimizers
() 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_scheduler_config
).Dictionary, with an
"optimizer"
key, and (optionally) a"lr_scheduler"
key whose value is a single LR scheduler orlr_scheduler_config
.Tuple of dictionaries as described above, with an optional
"frequency"
key.None - Fit will run without any optimizer.
The
lr_scheduler_config
is a dictionary which contains the scheduler and its associated configuration. The default configuration is shown below.lr_scheduler_config = { # 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_scheduler_config
contains the keyword"monitor"
set to the metric name that the scheduler should be conditioned on.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_scheduler_config
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 as needed.If learning rate scheduler is specified in
configure_optimizers()
with key"interval"
(default “epoch”) in the scheduler configuration, Lightning will call the scheduler’s.step()
method automatically in case of automatic optimization.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.
-
demo_video
(test_data, epoch=0, num_batches=100, show_video=False, show_pred=True, fps=30) This runs our classifier on several videos of the test dataset
- Parameters
test_data (object) – Dataloader
epoch (int, optional) – Index of the epoch. Used to name the video
num_batches (int, optional) – Number of batches used to create the video
show_video (boolean, optional) – Whether to display the demo
show_pred (boolean, optional) – Whether to show the prediction results as well. Set it to “False” to only inspect the input data
fps (int, optional) – Video output frame rate
-
forward
(batch) Same as
torch.nn.Module.forward()
.- Parameters
*args – Whatever you decide to pass into the forward method.
**kwargs – Keyword arguments are also possible.
- Returns
Your model’s output
-
load_pretrained
(checkpoint_path) Loads a pretrained detector (of this class) and transfer the weights to this module for fine-tuning.
In addition, it may remap the old classification weights if some overlap exists between old and new list of classes.
- Parameters
checkpoint_path (str) – path to checkpoint of pretrained detector.
-
test_epoch_end
(outputs) 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 of outputs you defined in
test_step_end()
, or if there are multiple dataloaders, a list containing a list of outputs for each dataloader- 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
(batch, batch_idx) 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
batch – The output of your
DataLoader
.batch_idx – The index of this batch.
dataloader_id – The index of the dataloader that produced this batch. (only if multiple test dataloaders used).
- 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=0): ...
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. We recommend setting the default value of 0 so that you can quickly switch between single and multiple dataloaders.# CASE 2: multiple test dataloaders def test_step(self, batch, batch_idx, dataloader_idx=0): # 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.
-
training_epoch_end
(outputs) 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 of outputs you defined in
training_step()
. If there are multiple optimizers or when usingtruncated_bptt_steps > 0
, the lists have the dimensions (n_batches, tbptt_steps, n_optimizers). Dimensions of length 1 are squeezed.- Returns
None
Note
If this method is not overridden, this won’t be called.
def training_epoch_end(self, training_step_outputs): # do something with all training_step outputs for out in training_step_outputs: ...
-
training_step
(batch, batch_nb) 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.batch_idx (
int
) – Integer displaying index of this batchoptimizer_idx (
int
) – When using multiple optimizers, this argument will also be present.hiddens (
Any
) – Passed in if :paramref:`~pytorch_lightning.core.module.LightningModule.truncated_bptt_steps` > 0.
- 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. This is only for automatic optimization.This is not supported for multi-GPU, TPU, IPU, or DeepSpeed.
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) loss = ... 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.
Note
When
accumulate_grad_batches
> 1, the loss returned here will be automatically normalized byaccumulate_grad_batches
internally.
-
validation_epoch_end
(outputs) 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 of outputs you defined in
validation_step()
, or if there are multiple dataloaders, a list containing a list of outputs for each dataloader.- 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
(batch, batch_idx) 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
batch – The output of your
DataLoader
.batch_idx – The index of this batch.
dataloader_idx – The index of the dataloader that produced this batch. (only if multiple val dataloaders used)
- 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=0): ...
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. We recommend setting the default value of 0 so that you can quickly switch between single and multiple dataloaders.# CASE 2: multiple validation dataloaders def validation_step(self, batch, batch_idx, dataloader_idx=0): # 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.