PyTorch Lightning DataModules¶
Author: PL team
License: CC BY-SA
Generated: 2021-08-31T13:56:06.824908
This notebook will walk you through how to start using Datamodules. With the release of pytorch-lightning version 0.9.0, we have included a new class called LightningDataModule to help you decouple data related hooks from your LightningModule. The most up to date documentation on datamodules can be found here.
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Setup¶
This notebook requires some packages besides pytorch-lightning.
[1]:
! pip install --quiet "torch>=1.6, <1.9" "torchvision" "torchmetrics>=0.3" "pytorch-lightning>=1.3"
Introduction¶
First, we’ll go over a regular LightningModule implementation without the use of a LightningDataModule
[2]:
import os
import torch
import torch.nn.functional as F
from pytorch_lightning import LightningDataModule, LightningModule, Trainer
from pytorch_lightning.metrics.functional import accuracy
from torch import nn
from torch.utils.data import DataLoader, random_split
from torchvision import transforms
# Note - you must have torchvision installed for this example
from torchvision.datasets import CIFAR10, MNIST
PATH_DATASETS = os.environ.get("PATH_DATASETS", ".")
AVAIL_GPUS = min(1, torch.cuda.device_count())
BATCH_SIZE = 256 if AVAIL_GPUS else 64
Defining the LitMNISTModel¶
Below, we reuse a LightningModule from our hello world tutorial that classifies MNIST Handwritten Digits.
Unfortunately, we have hardcoded dataset-specific items within the model, forever limiting it to working with MNIST Data. 😢
This is fine if you don’t plan on training/evaluating your model on different datasets. However, in many cases, this can become bothersome when you want to try out your architecture with different datasets.
[3]:
class LitMNIST(LightningModule):
def __init__(self, data_dir=PATH_DATASETS, hidden_size=64, learning_rate=2e-4):
super().__init__()
# We hardcode dataset specific stuff here.
self.data_dir = data_dir
self.num_classes = 10
self.dims = (1, 28, 28)
channels, width, height = self.dims
self.transform = transforms.Compose(
[
transforms.ToTensor(),
transforms.Normalize((0.1307,), (0.3081,)),
]
)
self.hidden_size = hidden_size
self.learning_rate = learning_rate
# Build model
self.model = nn.Sequential(
nn.Flatten(),
nn.Linear(channels * width * height, hidden_size),
nn.ReLU(),
nn.Dropout(0.1),
nn.Linear(hidden_size, hidden_size),
nn.ReLU(),
nn.Dropout(0.1),
nn.Linear(hidden_size, self.num_classes),
)
def forward(self, x):
x = self.model(x)
return F.log_softmax(x, dim=1)
def training_step(self, batch, batch_idx):
x, y = batch
logits = self(x)
loss = F.nll_loss(logits, y)
return loss
def validation_step(self, batch, batch_idx):
x, y = batch
logits = self(x)
loss = F.nll_loss(logits, y)
preds = torch.argmax(logits, dim=1)
acc = accuracy(preds, y)
self.log("val_loss", loss, prog_bar=True)
self.log("val_acc", acc, prog_bar=True)
return loss
def configure_optimizers(self):
optimizer = torch.optim.Adam(self.parameters(), lr=self.learning_rate)
return optimizer
####################
# DATA RELATED HOOKS
####################
def prepare_data(self):
# download
MNIST(self.data_dir, train=True, download=True)
MNIST(self.data_dir, train=False, download=True)
def setup(self, stage=None):
# Assign train/val datasets for use in dataloaders
if stage == "fit" or stage is None:
mnist_full = MNIST(self.data_dir, train=True, transform=self.transform)
self.mnist_train, self.mnist_val = random_split(mnist_full, [55000, 5000])
# Assign test dataset for use in dataloader(s)
if stage == "test" or stage is None:
self.mnist_test = MNIST(self.data_dir, train=False, transform=self.transform)
def train_dataloader(self):
return DataLoader(self.mnist_train, batch_size=128)
def val_dataloader(self):
return DataLoader(self.mnist_val, batch_size=128)
def test_dataloader(self):
return DataLoader(self.mnist_test, batch_size=128)
Training the ListMNIST Model¶
[4]:
model = LitMNIST()
trainer = Trainer(
max_epochs=2,
gpus=AVAIL_GPUS,
progress_bar_refresh_rate=20,
)
trainer.fit(model)
GPU available: True, used: True
TPU available: False, using: 0 TPU cores
IPU available: False, using: 0 IPUs
LOCAL_RANK: 0 - CUDA_VISIBLE_DEVICES: [0,1]
| Name | Type | Params
-------------------------------------
0 | model | Sequential | 55.1 K
-------------------------------------
55.1 K Trainable params
0 Non-trainable params
55.1 K Total params
0.220 Total estimated model params size (MB)
/home/AzDevOps_azpcontainer/.local/lib/python3.9/site-packages/pytorch_lightning/trainer/data_loading.py:105: UserWarning: The dataloader, val dataloader 0, does not have many workers which may be a bottleneck. Consider increasing the value of the `num_workers` argument` (try 12 which is the number of cpus on this machine) in the `DataLoader` init to improve performance.
rank_zero_warn(
/usr/local/lib/python3.9/dist-packages/deprecate/deprecation.py:115: LightningDeprecationWarning: The `accuracy` was deprecated since v1.3.0 in favor of `torchmetrics.functional.classification.accuracy.accuracy`. It will be removed in v1.5.0.
stream(template_mgs % msg_args)
/home/AzDevOps_azpcontainer/.local/lib/python3.9/site-packages/pytorch_lightning/trainer/data_loading.py:105: UserWarning: The dataloader, train dataloader, does not have many workers which may be a bottleneck. Consider increasing the value of the `num_workers` argument` (try 12 which is the number of cpus on this machine) in the `DataLoader` init to improve performance.
rank_zero_warn(
Using DataModules¶
DataModules are a way of decoupling data-related hooks from the LightningModule so you can develop dataset agnostic models.
Defining The MNISTDataModule¶
Let’s go over each function in the class below and talk about what they’re doing:
__init__Takes in a
data_dirarg that points to where you have downloaded/wish to download the MNIST dataset.Defines a transform that will be applied across train, val, and test dataset splits.
Defines default
self.dims, which is a tuple returned fromdatamodule.size()that can help you initialize models.
prepare_dataThis is where we can download the dataset. We point to our desired dataset and ask torchvision’s
MNISTdataset class to download if the dataset isn’t found there.Note we do not make any state assignments in this function (i.e.
self.something = ...)
setupLoads in data from file and prepares PyTorch tensor datasets for each split (train, val, test).
Setup expects a ‘stage’ arg which is used to separate logic for ‘fit’ and ‘test’.
If you don’t mind loading all your datasets at once, you can set up a condition to allow for both ‘fit’ related setup and ‘test’ related setup to run whenever
Noneis passed tostage.Note this runs across all GPUs and it is safe to make state assignments here
x_dataloadertrain_dataloader(),val_dataloader(), andtest_dataloader()all return PyTorchDataLoaderinstances that are created by wrapping their respective datasets that we prepared insetup()
[5]:
class MNISTDataModule(LightningDataModule):
def __init__(self, data_dir: str = PATH_DATASETS):
super().__init__()
self.data_dir = data_dir
self.transform = transforms.Compose(
[
transforms.ToTensor(),
transforms.Normalize((0.1307,), (0.3081,)),
]
)
# self.dims is returned when you call dm.size()
# Setting default dims here because we know them.
# Could optionally be assigned dynamically in dm.setup()
self.dims = (1, 28, 28)
self.num_classes = 10
def prepare_data(self):
# download
MNIST(self.data_dir, train=True, download=True)
MNIST(self.data_dir, train=False, download=True)
def setup(self, stage=None):
# Assign train/val datasets for use in dataloaders
if stage == "fit" or stage is None:
mnist_full = MNIST(self.data_dir, train=True, transform=self.transform)
self.mnist_train, self.mnist_val = random_split(mnist_full, [55000, 5000])
# Assign test dataset for use in dataloader(s)
if stage == "test" or stage is None:
self.mnist_test = MNIST(self.data_dir, train=False, transform=self.transform)
def train_dataloader(self):
return DataLoader(self.mnist_train, batch_size=BATCH_SIZE)
def val_dataloader(self):
return DataLoader(self.mnist_val, batch_size=BATCH_SIZE)
def test_dataloader(self):
return DataLoader(self.mnist_test, batch_size=BATCH_SIZE)
Defining the dataset agnostic LitModel¶
Below, we define the same model as the LitMNIST model we made earlier.
However, this time our model has the freedom to use any input data that we’d like 🔥.
[6]:
class LitModel(LightningModule):
def __init__(self, channels, width, height, num_classes, hidden_size=64, learning_rate=2e-4):
super().__init__()
# We take in input dimensions as parameters and use those to dynamically build model.
self.channels = channels
self.width = width
self.height = height
self.num_classes = num_classes
self.hidden_size = hidden_size
self.learning_rate = learning_rate
self.model = nn.Sequential(
nn.Flatten(),
nn.Linear(channels * width * height, hidden_size),
nn.ReLU(),
nn.Dropout(0.1),
nn.Linear(hidden_size, hidden_size),
nn.ReLU(),
nn.Dropout(0.1),
nn.Linear(hidden_size, num_classes),
)
def forward(self, x):
x = self.model(x)
return F.log_softmax(x, dim=1)
def training_step(self, batch, batch_idx):
x, y = batch
logits = self(x)
loss = F.nll_loss(logits, y)
return loss
def validation_step(self, batch, batch_idx):
x, y = batch
logits = self(x)
loss = F.nll_loss(logits, y)
preds = torch.argmax(logits, dim=1)
acc = accuracy(preds, y)
self.log("val_loss", loss, prog_bar=True)
self.log("val_acc", acc, prog_bar=True)
return loss
def configure_optimizers(self):
optimizer = torch.optim.Adam(self.parameters(), lr=self.learning_rate)
return optimizer
Training the LitModel using the MNISTDataModule¶
Now, we initialize and train the LitModel using the MNISTDataModule’s configuration settings and dataloaders.
[7]:
# Init DataModule
dm = MNISTDataModule()
# Init model from datamodule's attributes
model = LitModel(*dm.size(), dm.num_classes)
# Init trainer
trainer = Trainer(
max_epochs=3,
progress_bar_refresh_rate=20,
gpus=AVAIL_GPUS,
)
# Pass the datamodule as arg to trainer.fit to override model hooks :)
trainer.fit(model, dm)
GPU available: True, used: True
TPU available: False, using: 0 TPU cores
IPU available: False, using: 0 IPUs
LOCAL_RANK: 0 - CUDA_VISIBLE_DEVICES: [0,1]
| Name | Type | Params
-------------------------------------
0 | model | Sequential | 55.1 K
-------------------------------------
55.1 K Trainable params
0 Non-trainable params
55.1 K Total params
0.220 Total estimated model params size (MB)
Defining the CIFAR10 DataModule¶
Lets prove the LitModel we made earlier is dataset agnostic by defining a new datamodule for the CIFAR10 dataset.
[8]:
class CIFAR10DataModule(LightningDataModule):
def __init__(self, data_dir: str = "./"):
super().__init__()
self.data_dir = data_dir
self.transform = transforms.Compose(
[
transforms.ToTensor(),
transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5)),
]
)
self.dims = (3, 32, 32)
self.num_classes = 10
def prepare_data(self):
# download
CIFAR10(self.data_dir, train=True, download=True)
CIFAR10(self.data_dir, train=False, download=True)
def setup(self, stage=None):
# Assign train/val datasets for use in dataloaders
if stage == "fit" or stage is None:
cifar_full = CIFAR10(self.data_dir, train=True, transform=self.transform)
self.cifar_train, self.cifar_val = random_split(cifar_full, [45000, 5000])
# Assign test dataset for use in dataloader(s)
if stage == "test" or stage is None:
self.cifar_test = CIFAR10(self.data_dir, train=False, transform=self.transform)
def train_dataloader(self):
return DataLoader(self.cifar_train, batch_size=BATCH_SIZE)
def val_dataloader(self):
return DataLoader(self.cifar_val, batch_size=BATCH_SIZE)
def test_dataloader(self):
return DataLoader(self.cifar_test, batch_size=BATCH_SIZE)
Training the LitModel using the CIFAR10DataModule¶
Our model isn’t very good, so it will perform pretty badly on the CIFAR10 dataset.
The point here is that we can see that our LitModel has no problem using a different datamodule as its input data.
[9]:
dm = CIFAR10DataModule()
model = LitModel(*dm.size(), dm.num_classes, hidden_size=256)
trainer = Trainer(
max_epochs=5,
progress_bar_refresh_rate=20,
gpus=AVAIL_GPUS,
)
trainer.fit(model, dm)
GPU available: True, used: True
TPU available: False, using: 0 TPU cores
IPU available: False, using: 0 IPUs
Files already downloaded and verified
Files already downloaded and verified
LOCAL_RANK: 0 - CUDA_VISIBLE_DEVICES: [0,1]
| Name | Type | Params
-------------------------------------
0 | model | Sequential | 855 K
-------------------------------------
855 K Trainable params
0 Non-trainable params
855 K Total params
3.420 Total estimated model params size (MB)
Congratulations - Time to Join the Community!¶
Congratulations on completing this notebook tutorial! If you enjoyed this and would like to join the Lightning movement, you can do so in the following ways!
Star Lightning on GitHub¶
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Join our Slack!¶
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Contributions !¶
The best way to contribute to our community is to become a code contributor! At any time you can go to Lightning or Bolt GitHub Issues page and filter for “good first issue”.
You can also contribute your own notebooks with useful examples !
Great thanks from the entire Pytorch Lightning Team for your interest !¶
