book

Deep Learning for Coders with fastai and PyTorch

by Jeremy Howard, Sylvain Gugger

July 2020

Intermediate to advanced

621 pages

16h 47m

English

O'Reilly Media, Inc.

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Who This Book Is ForWhat You Need to KnowWhat You Will LearnO’Reilly Online LearningHow to Contact Us
Deep Learning Is for EveryoneNeural Networks: A Brief HistoryWho We AreHow to Learn Deep LearningYour Projects and Your MindsetThe Software: PyTorch, fastai, and Jupyter (And Why It Doesn’t Matter)Your First ModelGetting a GPU Deep Learning ServerRunning Your First NotebookWhat Is Machine Learning?What Is a Neural Network?A Bit of Deep Learning JargonLimitations Inherent to Machine LearningHow Our Image Recognizer WorksWhat Our Image Recognizer LearnedImage Recognizers Can Tackle Non-Image TasksJargon RecapDeep Learning Is Not Just for Image ClassificationValidation Sets and Test SetsUse Judgment in Defining Test SetsA Choose Your Own Adventure MomentQuestionnaireFurther Research
The Practice of Deep LearningStarting Your ProjectThe State of Deep LearningThe Drivetrain ApproachGathering DataFrom Data to DataLoadersData AugmentationTraining Your Model, and Using It to Clean Your DataTurning Your Model into an Online ApplicationUsing the Model for InferenceCreating a Notebook App from the ModelTurning Your Notebook into a Real AppDeploying Your AppHow to Avoid DisasterUnforeseen Consequences and Feedback LoopsGet Writing!QuestionnaireFurther Research
Key Examples for Data EthicsBugs and Recourse: Buggy Algorithm Used for Healthcare BenefitsFeedback Loops: YouTube’s Recommendation SystemBias: Professor Latanya Sweeney “Arrested”Why Does This Matter?Integrating Machine Learning with Product DesignTopics in Data EthicsRecourse and AccountabilityFeedback LoopsBiasDisinformationIdentifying and Addressing Ethical IssuesAnalyze a Project You Are Working OnProcesses to ImplementThe Power of DiversityFairness, Accountability, and TransparencyRole of PolicyThe Effectiveness of RegulationRights and PolicyCars: A Historical PrecedentConclusionQuestionnaireFurther ResearchDeep Learning in Practice: That’s a Wrap!
Pixels: The Foundations of Computer VisionFirst Try: Pixel SimilarityNumPy Arrays and PyTorch TensorsComputing Metrics Using BroadcastingStochastic Gradient DescentCalculating GradientsStepping with a Learning RateAn End-to-End SGD ExampleSummarizing Gradient DescentThe MNIST Loss FunctionSigmoidSGD and Mini-BatchesPutting It All TogetherCreating an OptimizerAdding a NonlinearityGoing DeeperJargon RecapQuestionnaireFurther Research
From Dogs and Cats to Pet BreedsPresizingChecking and Debugging a DataBlockCross-Entropy LossViewing Activations and LabelsSoftmaxLog LikelihoodTaking the logModel InterpretationImproving Our ModelThe Learning Rate FinderUnfreezing and Transfer LearningDiscriminative Learning RatesSelecting the Number of EpochsDeeper ArchitecturesConclusionQuestionnaireFurther Research
Multi-Label ClassificationThe DataConstructing a DataBlockBinary Cross EntropyRegressionAssembling the DataTraining a ModelConclusionQuestionnaireFurther Research

ImagenetteNormalizationProgressive ResizingTest Time AugmentationMixupLabel SmoothingConclusionQuestionnaireFurther Research
A First Look at the DataLearning the Latent FactorsCreating the DataLoadersCollaborative Filtering from ScratchWeight DecayCreating Our Own Embedding ModuleInterpreting Embeddings and BiasesUsing fastai.collabEmbedding DistanceBootstrapping a Collaborative Filtering ModelDeep Learning for Collaborative FilteringConclusionQuestionnaireFurther Research
Categorical EmbeddingsBeyond Deep LearningThe DatasetKaggle CompetitionsLook at the DataDecision TreesHandling DatesUsing TabularPandas and TabularProcCreating the Decision TreeCategorical VariablesRandom ForestsCreating a Random ForestOut-of-Bag ErrorModel InterpretationTree Variance for Prediction ConfidenceFeature ImportanceRemoving Low-Importance VariablesRemoving Redundant FeaturesPartial DependenceData LeakageTree InterpreterExtrapolation and Neural NetworksThe Extrapolation ProblemFinding Out-of-Domain DataUsing a Neural NetworkEnsemblingBoostingCombining Embeddings with Other MethodsConclusionQuestionnaireFurther Research
Text PreprocessingTokenizationWord Tokenization with fastaiSubword TokenizationNumericalization with fastaiPutting Our Texts into Batches for a Language ModelTraining a Text ClassifierLanguage Model Using DataBlockFine-Tuning the Language ModelSaving and Loading ModelsText GenerationCreating the Classifier DataLoadersFine-Tuning the ClassifierDisinformation and Language ModelsConclusionQuestionnaireFurther Research
Going Deeper into fastai’s Layered APITransformsWriting Your Own TransformPipelineTfmdLists and Datasets: Transformed CollectionsTfmdListsDatasetsApplying the Mid-Level Data API: SiamesePairConclusionQuestionnaireFurther ResearchUnderstanding fastai’s Applications: Wrap Up
The DataOur First Language Model from ScratchOur Language Model in PyTorchOur First Recurrent Neural NetworkImproving the RNNMaintaining the State of an RNNCreating More SignalMultilayer RNNsThe ModelExploding or Disappearing ActivationsLSTMBuilding an LSTM from ScratchTraining a Language Model Using LSTMsRegularizing an LSTMDropoutActivation Regularization and Temporal Activation RegularizationTraining a Weight-Tied Regularized LSTMConclusionQuestionnaireFurther Research
The Magic of ConvolutionsMapping a Convolutional KernelConvolutions in PyTorchStrides and PaddingUnderstanding the Convolution EquationsOur First Convolutional Neural NetworkCreating the CNNUnderstanding Convolution ArithmeticReceptive FieldsA Note About TwitterColor ImagesImproving Training StabilityA Simple BaselineIncrease Batch Size1cycle TrainingBatch NormalizationConclusionQuestionnaireFurther Research
Going Back to ImagenetteBuilding a Modern CNN: ResNetSkip ConnectionsA State-of-the-Art ResNetBottleneck LayersConclusionQuestionnaireFurther Research
Computer Visioncnn_learnerunet_learnerA Siamese NetworkNatural Language ProcessingTabularConclusionQuestionnaireFurther Research
Establishing a BaselineA Generic OptimizerMomentumRMSPropAdamDecoupled Weight DecayCallbacksCreating a CallbackCallback Ordering and ExceptionsConclusionQuestionnaireFurther ResearchFoundations of Deep Learning: Wrap Up
Building a Neural Net Layer from ScratchModeling a NeuronMatrix Multiplication from ScratchElementwise ArithmeticBroadcastingEinstein SummationThe Forward and Backward PassesDefining and Initializing a LayerGradients and the Backward PassRefactoring the ModelGoing to PyTorchConclusionQuestionnaireFurther Research
CAM and HooksGradient CAMConclusionQuestionnaireFurther Research
DataDatasetModule and ParameterSimple CNNLossLearnerCallbacksScheduling the Learning RateConclusionQuestionnaireFurther Research
Blogging with GitHub PagesCreating the RepositorySetting Up Your Home PageCreating PostsSynchronizing GitHub and Your ComputerJupyter for Blogging
Data ScientistsStrategyDataAnalyticsImplementationMaintenanceConstraints

Content preview from Deep Learning for Coders with fastai and PyTorch

Chapter 19. A fastai Learner from Scratch

This final chapter (other than the conclusion and the online chapters) is going to look a bit different. It contains far more code and far less prose than the previous chapters. We will introduce new Python keywords and libraries without discussing them. This chapter is meant to be the start of a significant research project for you. You see, we are going to implement many of the key pieces of the fastai and PyTorch APIs from scratch, building on nothing other than the components that we developed in Chapter 17! The key goal here is to end up with your own Learner class and some callbacks—enough to be able to train a model on Imagenette, including examples of each of the key techniques we’ve studied. On the way to building Learner, we will create our own versions of Module, Parameter and a parallel DataLoader so you’ll have a very good idea of what those PyTorch classes do.

The end-of-chapter questionnaire is particularly important for this chapter. This is where we will be pointing you in the many interesting directions that you could take, using this chapter as your starting point. We suggest that you follow along with this chapter on your computer, and do lots of experiments, web searches, and whatever else you need to understand what’s going on. You’ve built up the skills and expertise to do this in the rest of this book, so we think you are going to do great!

Let’s begin by gathering (manually) some data.