Daniel Voigt Godoy - Deep Learning with PyTorch Step-by-Step A Beginner’s Guide-leanpub

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RecapFirst of all, congratulations are in order: You have successfully implemented a fullyfunctioning model and training loop in PyTorch!We have covered a lot of ground in this first chapter:• implementing a linear regression in Numpy using gradient descent• creating tensors in PyTorch, sending them to a device, and making parametersout of them• understanding PyTorch’s main feature, autograd, to perform automaticdifferentiation using its associated properties and methods, like backward(),grad, zero_(), and no_grad()• visualizing the dynamic computation graph associated with a sequence ofoperations• creating an optimizer to simultaneously update multiple parameters, using itsstep() and zero_grad() methods• creating a loss function using PyTorch’s corresponding higher-order function(more on that topic in the next chapter)• understanding PyTorch’s Module class and creating your own models,implementing __init__() and forward() methods, and making use of its builtinparameters() and state_dict() methods• transforming the original Numpy implementation into a PyTorch one using theelements above• realizing the importance of including model.train() inside the training loop(never forget that!)• implementing nested and sequential models using PyTorch’s layers• putting it all together into neatly organized code divided into three distinctparts: data preparation, model configuration, and model trainingYou are now ready for the next chapter. We’ll see more of PyTorch’s capabilities,and we’ll further develop our training loop so it can be used for different problemsand models. You’ll be building your own, small draft of a library for training deeplearning models.[39] https://github.com/dvgodoy/PyTorchStepByStep/blob/master/Chapter01.ipynb[40] https://colab.research.google.com/github/dvgodoy/PyTorchStepByStep/blob/master/Chapter01.ipynbRecap | 121
[41] https://en.wikipedia.org/wiki/Gaussian_noise[42] https://bit.ly/2XZXjnk[43] https://bit.ly/3fjCSHR[44] https://bit.ly/2Y0lhPn[45] https://bit.ly/2UDXDWM[46] https://twitter.com/alecrad[47] http://cs231n.stanford.edu/[48] https://realpython.com/python3-object-oriented-programming/[49] https://realpython.com/python-super/[50] https://ipython.readthedocs.io/en/stable/interactive/magics.html[51] https://bit.ly/30GH0vO[52] https://bit.ly/3g1eQCm122 | Chapter 1: A Simple Regression Problem
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Deep Learning with PyTorchStep-by-S
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"What I cannot create, I do not und
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Train-Validation-Test Split. . . .
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Random Split. . . . . . . . . . . .
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The Precision Quirk . . . . . . . .
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A REAL Filter . . . . . . . . . . .
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Jupyter Notebook . . . . . . . . .
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Stacked RNN . . . . . . . . . . . .
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Attention Mechanism . . . . . . . .
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4. Positional Encoding. . . . . . .
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Model Configuration & Training . .
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AcknowledgementsFirst and foremost,
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Frequently Asked Questions (FAQ)Why
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There is yet another advantage of f
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• Classes and methods are written
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What’s Next?It’s time to set up
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After choosing a repository, it wil
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1. AnacondaIf you don’t have Anac
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3. PyTorchPyTorch is the coolest de
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(pytorchbook) C:\> conda install py
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(pytorchbook)$ pip install torchviz
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7. JupyterAfter cloning the reposit
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Part IFundamentals| 21
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notebook. If not, just click on Cha
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Also, let’s say that, on average,
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There is one exception to the "alwa
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Random Initialization1 # Step 0 - I
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Batch, Mini-batch, and Stochastic G
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Outputarray([[-2. , -1.94, -1.88, .
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one matrix for each data point, eac
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Sure, different values of b produce
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Output-3.044811379650508 -1.8337537
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each parameter using the chain rule
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What’s the impact of one update o
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gradients, we know we need to take
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Very High Learning RateWait, it may
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true_b = 1true_w = 2N = 100# Data G
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Let’s look at the cross-sections
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Zero Mean and Unit Standard Deviati
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Sure, in the real world, you’ll n
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computing the loss, as shown in the
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• visualizing the effects of usin
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If you’re using Jupyter’s defau
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Notebook Cell 1.1 - Splitting synth
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Step 2# Step 2 - Computing the loss
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Output[0.49671415] [-0.1382643][0.8
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Notebook Cell 1.2 - Implementing gr
Page 96 and 97: # Sanity Check: do we get the same
Page 98 and 99: Outputtensor(3.1416)tensor([1, 2, 3
Page 100 and 101: Outputtensor([[1., 2., 1.],[1., 1.,
Page 102 and 103: dummy_array = np.array([1, 2, 3])du
Page 104 and 105: n_cudas = torch.cuda.device_count()
Page 106 and 107: back_to_numpy = x_train_tensor.nump
Page 108 and 109: I am assuming you’d like to use y
Page 110 and 111: Outputtensor([0.1940], device='cuda
Page 112 and 113: print(error.requires_grad, yhat.req
Page 114 and 115: Output(tensor([0.], device='cuda:0'
Page 116 and 117: 56 # need to tell it to let it go..
Page 118 and 119: computation.If you chose "Local Ins
Page 120 and 121: Figure 1.6 - Now parameter "b" does
Page 122 and 123: There are many optimizers: SGD is t
Page 124 and 125: 41 optimizer.zero_grad() 34243 prin
Page 126 and 127: Notebook Cell 1.8 - PyTorch’s los
Page 128 and 129: Outputarray(0.00804466, dtype=float
Page 130 and 131: Let’s build a proper (yet simple)
Page 132 and 133: "What do we need this for?"It turns
Page 134 and 135: 1 Instantiating a model2 What IS th
Page 136 and 137: In the __init__() method, we create
Page 138 and 139: LayersA Linear model can be seen as
Page 140 and 141: There are MANY different layers tha
Page 142 and 143: We use magic, just like that:%run -
Page 144 and 145: • Step 1: compute model’s predi
Page 148 and 149: Chapter 2Rethinking the Training Lo
Page 150 and 151: Let’s take a look at the code onc
Page 152 and 153: Higher-Order FunctionsAlthough this
Page 154 and 155: def exponentiation_builder(exponent
Page 156 and 157: Apart from returning the loss value
Page 158 and 159: Our code should look like this; see
Page 160 and 161: There is no need to load the whole
Page 162 and 163: but if we want to get serious about
Page 164 and 165: How does this change our code so fa
Page 166 and 167: Run - Model Training V2%run -i mode
Page 168 and 169: piece of code that’s going to be
Page 170 and 171: for it. We could do the same for th
Page 172 and 173: EvaluationHow can we evaluate the m
Page 174 and 175: And then, we update our model confi
Page 176 and 177: Run - Model Training V4%run -i mode
Page 178 and 179: Loading Extension# Load the TensorB
Page 180 and 181: browser, you’ll likely see someth
Page 182 and 183: model’s graph (not quite the same
Page 184 and 185: Figure 2.5 - Scalars on TensorBoard
Page 186 and 187: Define - Model Training V51 %%write
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Page 190 and 191: The procedure is exactly the same,
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Page 194 and 195: After recovering our model’s stat
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Run - Model Configuration V31 # %lo
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This is the general structure you
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Chapter 2.1Going ClassySpoilersIn t
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# A completely empty (and useless)
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# These attributes are defined here
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# Creates the train_step function f
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# Builds function that performs a s
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setattrThe setattr function sets th
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See? We effectively modified the un
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the random seed as arguments.This s
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The current state of development of
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Lossesdef plot_losses(self):fig = p
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Run - Data Preparation V21 # %load
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Model TrainingWe start by instantia
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Making PredictionsLet’s make up s
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OutputOrderedDict([('0.weight', ten
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Run - Data Preparation V21 # %load
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• defining our StepByStep class
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import numpy as npimport torchimpor
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Next, we’ll standardize the featu
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Equation 3.1 - A linear regression
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The odds ratio is given by the rati
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As expected, probabilities that add
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Sigmoid Functiondef sigmoid(z):retu
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A picture is worth a thousand words
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OutputOrderedDict([('linear.weight'
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The first summation adds up the err
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IMPORTANT: Make sure to pass the pr
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To make it clear: In this chapter,
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argument of nn.BCEWithLogitsLoss().
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It is not that hard, to be honest.
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Figure 3.6 - Training and validatio
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Outputarray([[0.5504593 ],[0.949995
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decision boundary.Look at the expre
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Are my data points separable?That
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model = nn.Sequential()model.add_mo
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It looks like this:Figure 3.10 - Sp
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True and False Positives and Negati
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tpr_fpr(cm_thresh50)Output(0.909090
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The trade-off between precision and
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Figure 3.13 - Using a low threshold
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Figure 3.16 - Trade-offs for two di
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thresholds do not necessarily inclu
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actual data, it is as bad as it can
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If you want to learn more about bot
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Model Training1 n_epochs = 10023 sb
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step in your journey! What’s next
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Chapter 4Classifying ImagesSpoilers
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Data GenerationOur images are quite
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Images and ChannelsIn case you’re
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image_rgb = np.stack([image_r, imag
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That’s fairly straightforward; we
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• Transformations based on Tensor
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position of an object in a picture
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Outputtensor([[[0., 0., 0., 1., 0.]
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Outputtensor([[[-1., -1., -1., 1.,
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We can convert the former into the
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composer = Compose([RandomHorizonta
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Output<torch.utils.data.dataset.Sub
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train_composer = Compose([RandomHor
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The minority class should have the
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train_loader = DataLoader(dataset=t
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implemented in Chapter 2.1? Let’s
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Let’s take one mini-batch of imag
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What does our model look like? Visu
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Model TrainingLet’s train our mod
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preceding hidden layer to compute i
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fig = sbs_nn.plot_losses()Figure 4.
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Equation 4.2 - Equivalence of deep
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w_nn_equiv = w_nn_output.mm(w_nn_hi
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Weights as PixelsDuring data prepar
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is only 0.25 (for z = 0) and that i
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nn.Tanh()(dummy_z)Outputtensor([-0.
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dummy_z = torch.tensor([-3., 0., 3.
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As you can see, in PyTorch the coef
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Figure 4.16 - Deep model (for real)
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Figure 4.18 - Losses (before and af
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Equation 4.3 - Activation functions
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Helper Function #41 def index_split
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Model Configuration1 # Sets learnin
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Bonus ChapterFeature SpaceThis chap
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Affine TransformationsAn affine tra
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Figure B.3 - Annotated model diagra
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Figure B.5 - In the beginning…But
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OK, now we can clearly see a differ
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In the model above, the sigmoid fun
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the more dimensions, the more separ
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import randomimport numpy as npfrom
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identity = np.array([[[[0, 0, 0],[0
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Figure 5.4 - Striding the image, on
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Output-----------------------------
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Outputtensor([[[[9., 5., 0., 7.],[0
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OutputParameter containing:tensor([
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Moreover, notice that if we were to
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In code, as usual, PyTorch gives us
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Outputtensor([[[[5., 5., 0., 8., 7.
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edge = np.array([[[[0, 1, 0],[1, -4
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A pooling kernel of two-by-two resu
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Outputtensor([[22., 23., 11., 24.,
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Figure 5.15 - LeNet-5 architectureS
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• second block: produces 16-chann
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Transformed Dataset1 class Transfor
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LossNew problem, new loss. Since we
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Outputtensor([4.0000, 1.0000, 0.500
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The loss only considers the predict
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Outputtensor([[-1.5229, -0.3146, -2
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IMPORTANT: I can’t stress this en
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figures at the beginning of this ch
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The three units in the output layer
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StepByStep Method@staticmethoddef _
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The meow() method is totally indepe
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StepByStep Methoddef visualize_filt
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dummy_model = nn.Linear(1, 1)dummy_
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dummy_listOutput[(Linear(in_feature
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Output{Conv2d(1, 1, kernel_size=(3,
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will be the externally defined vari
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Removing Hookssbs_cnn1.remove_hooks
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return figsetattr(StepByStep, 'visu
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Figure 5.22 - Feature maps (classif
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classification: The predicted class
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convolutional layers to our model a
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Capturing Outputsfeaturizer_layers
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the filters learned by the model pr
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given chapter are imported at its v
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Data PreparationThe data preparatio
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model anyway. We’ll use it to com
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StepByStep Method@staticmethoddef m
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"What’s wrong with the colors?"Th
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three_channel_filter = np.array([[[
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Fancier Model (Constructor)class CN
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Fancier Model (Classifier)def class
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torch.manual_seed(44)dropping_model
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Outputtensor([0.1000, 0.2000, 0.300
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Figure 6.8 - Output distribution fo
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Adaptive moment estimation (Adam) u
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torch.manual_seed(13)# Model Config
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Outputtorch.Size([5, 3, 3, 3])Its s
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Choosing a learning rate that works
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Higher-Order Learning Rate Function
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Perfect! Now let’s build the actu
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ax.set_xlabel('Learning Rate')ax.se
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LRFinderThe function we’ve implem
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value in our moving average has an
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Figure 6.15 - Distribution of weigh
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In code, the implementation of the
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As expected, the EWMA without corre
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optimizer = optim.Adam(model.parame
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IMPORTANT: The logging function mus
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Output{'state': {140601337662512: {
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different optimizer, set them to ca
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• dampening: dampening factor for
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Figure 6.20 - Paths taken by SGD (w
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Equation 6.16 - Looking aheadOnce N
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Figure 6.22 - Path taken by each SG
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for epoch in range(4):# training lo
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course) up to a given number of epo
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Next, we create a protected method
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Mini-Batch SchedulersThese schedule
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Schedulers in StepByStep — Part I
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Scheduler PathsBefore trying out a
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After applying each scheduler to SG
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Data Preparation1 # Loads temporary
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Figure 6.31 - LossesEvaluationprint
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[96] http://www.samkass.com/theorie
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ImportsFor the sake of organization
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ILSVRC-2012The 2012 edition [111] o
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remained unchanged.ResNet (MSRA Tea
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Transfer Learning in PracticeIn Cha
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dropout. You’re already familiar
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OutputDownloading: "https://downloa
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Replacing the "Top" of the Model1 a
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Model Size Classifier Layer(s) Repl
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Model TrainingWe have everything se
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"Removing" the Top Layer1 alex.clas
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torch.save(train_preproc.tensors, '
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Outputtensor([[109, 124],[124, 124]
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Model Configuration1 optimizer_mode
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Figure 7.4 - 1x1 convolutionThe inp
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The weights used by PIL are 0.299 f
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• reduce the number of output cha
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The constructor method defines the
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Does it sound familiar? That’s wh
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and w to represent these parameters
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A mini-batch of size 64 is small en
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normed1 = batch_normalizer(batch1[0
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OutputOrderedDict([('running_mean',
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OutputOrderedDict([('running_mean',
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batch_normalizer = nn.BatchNorm2d(n
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torch.manual_seed(23)dummy_points =
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np.concatenate([dummy_points[:5].nu
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Another advantage of these shortcut
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It should be pretty clear, except f
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Data Preparation1 # ImageNet statis
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Data Preparation — Preprocessing1
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• freezing the layers of the mode
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Extra ChapterVanishing and Explodin
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discussing it, let me illustrate it
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Model Configuration (2)1 loss_fn =
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weights. If done properly, the init
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just did), or, if you are training
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Figure E.3 - The effect of batch no
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Model Configuration1 torch.manual_s
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torch.manual_seed(42)parm = nn.Para
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(and only if) the norm exceeds the
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if callable(self.clipping): 1self.c
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Moreover, let’s use a ten times h
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Clipping with HooksFirst, we reset
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• visualizing the difference betw
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Chapter 8SequencesSpoilersIn this c
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Before shuffling, the pixels were o
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And then let’s visualize the firs
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sequence so far, and a data point f
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Considering this, the not "unrolled
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linear_input = nn.Linear(n_features
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Outputtensor([[0.3924, 0.8146]], gr
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Now we’re talking! The last hidde
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Let’s take a look at the RNN’s
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◦ The initial hidden state, which
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batch_first argument to True so we
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OutputOrderedDict([('weight_ih_l0',
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out, hidden = rnn_stacked(x)out, hi
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_l0_reverse).Once again, let’s cr
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For bidirectional RNNs, the last el
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Model Configuration1 class SquareMo
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StepByStep.loader_apply(test_loader
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Figure 8.14 - Final hidden states f
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Figure 8.16 - Transforming the hidd
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Since the RNN cell has both of them
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Every gate worthy of its name will
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• For r=0 and z=0, the cell becom
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In code, we can use split() to get
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Let’s pause for a moment here. Fi
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Square Model II — The QuickeningT
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Outputtensor([[53, 53],[75, 75]])Th
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Figure 8.22 - Transforming the hidd
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Equation 8.9 - LSTM—candidate hid
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Now, let’s visualize the internal
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OutputOrderedDict([('weight_ih', te
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def forget_gate(h, x):thf = f_hidde
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Outputtensor([[-5.4936e-02, -8.3816
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1 First change: from RNN to LSTM2 S
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Like the GRU, the LSTM presents fou
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Output-----------------------------
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Before moving on to packed sequence
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column-wise fashion, from top to bo
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does match the last output.• No,
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So, to actually get the last output
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Data Preparation1 class CustomDatas
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OutputPackedSequence(data=tensor([[
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Model Configuration & TrainingWe ca
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size = 5weight = torch.ones(size) *
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torch.manual_seed(17)conv_seq = nn.
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Figure 8.32 - Applying dilated filt
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Model Configuration1 torch.manual_s
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We can actually find an expression
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Data Preparation1 def pack_collate(
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and variable-length sequences.Model
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• generating variable-length sequ
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import copyimport numpy as npimport
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Figure 9.3 - Sequence datasetThe co
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coordinates of a "perfect" square a
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Let’s pretend for a moment that t
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to initialize the hidden state and
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predictions in previous steps have
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the second set of predicted coordin
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Let’s create an instance of the m
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Model Configuration & TrainingThe m
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Sure, we can!AttentionHere is a (no
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based on "the" and "zone," I’ve j
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Figure 9.12 - Matching a query to t
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Outputtensor([[[ 0.0832, -0.0356],[
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utmost importance for the correct i
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Its formula is:Equation 9.3 - Cosin
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second hidden state contributes to
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Outputtensor([[[ 0.5475, 0.0875, -1
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alphas = F.softmax(scaled_products,
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Outputtensor([[[ 0.2138, -0.3175]]]
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Attention Mechanism1 class Attentio
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"Why would I want to force it to do
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1 Sets attention module and adjusts
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encdec = EncoderDecoder(encoder, de
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fig = sbs_seq_attn.plot_losses()Fig
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Figure 9.20 - Attention scoresSee?
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Wide vs Narrow AttentionThis mechan
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"What’s so special about it?"Even
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Once again, the affine transformati
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Next, we shift our focus to the sel
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Encoder + Self-Attention1 class Enc
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Figure 9.27 - Encoder with self- an
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The figure below depicts the self-a
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shifted_seq = torch.cat([source_seq
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Equation 9.17 - Decoder’s (masked
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At evaluation / prediction time we
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Outputtensor([[[0.4132, 0.3728],[0.
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Figure 9.33 - Encoder + decoder + a
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64 return outputsThe encoder-decode
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Figure 9.34 - Losses—encoder + de
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curse. On the one hand, it makes co
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"Are we done now? Is this good enou
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Figure 9.46 - Consistent distancesA
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Let’s recap what we’ve already
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Let’s see it in code:max_len = 10
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Let’s put it all together into a
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Outputtensor([[[-1.0000, 0.0000],[-
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Decoder with Positional Encoding1 c
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Visualizing PredictionsLet’s plot
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Next, we’re moving on to the thre
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Data Generation & Preparation1 # Tr
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59 self.trg_masks)60 else:61 # Deco
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Model Configuration1 class EncoderS
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1617 @property18 def alphas(self):1
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Output(0.016193246061448008, 0.0341
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sequential order of the data• fig
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following imports:import copyimport
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Figure 10.2 - Chunking: the wrong a
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chunks to compute the other half of
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67 # N, L, n_heads, d_k68 context =
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dummy_points = torch.randn(16, 2, 4
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Stacking Encoders and DecodersLet
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"… with great depth comes great c
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Transformer EncoderWe’ll be repre
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Let’s see it in code, starting wi
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Transformer Encoder1 class EncoderT
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of the encoder-decoder (or Transfor
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In PyTorch, the decoder "layer" is
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In PyTorch, the decoder is implemen
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Equation 10.7 - Data points' means
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layer_norm = nn.LayerNorm(d_model)n
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Figure 10.10 - Layer norm vs batch
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Outputtensor([[[ 1.4636, 2.3663],[
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The TransformerLet’s start with t
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"values") in the decoder.• decode
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Data Preparation1 # Generating trai
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Figure 10.15 - Losses—Transformer
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• First, and most important, PyTo
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decode(), with a single one, encode
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46 for i in range(self.target_len):
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Figure 10.18 - Losses - PyTorch’s
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Figure 10.20 - Sample image—label
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4041 # Builds a weighted random sam
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Figure 10.23 - Sample image—split
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Einops"There is more than one way t
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Figure 10.26 - Two patch embeddings
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Now each sequence has ten elements,
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It takes an instance of a Transform
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Putting It All TogetherIn this chap
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1. Encoder-DecoderThe encoder-decod
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This is the actual encoder-decoder
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3. DecoderThe Transformer decoder h
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5. Encoder "Layer"The encoder "laye
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7. "Sub-Layer" WrapperThe "sub-laye
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8. Multi-Headed AttentionThe multi-
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Model Configuration & TrainingModel
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• training the Transformer to tac
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Part IVNatural Language Processing|
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Additional SetupThis is a special c
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"Down the Yellow Brick Rabbit Hole"
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The actual texts of the books are c
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"What is this punkt?"That’s the P
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14 # If there is a configuration fi
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Sentence Tokenization in spaCyBy th
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AttributesThe Dataset has many attr
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Output{'labels': 1,'sentence': 'The
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elements from the text. But preproc
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Data AugmentationLet’s briefly ad
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The corpora’s dictionary is not a
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Finally, if we want to convert a li
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Once we’re happy with the size an
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from transformers import BertTokeni
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"What about the separation token?"T
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The last output, attention_mask, wo
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Outputtensor([[ 3, 27, 1, ..., 0, 0
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vector, right? And our vocabulary i
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Maybe you filled this blank in with
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Continuous Bag-of-Words (CBoW)In th
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That’s a fairly simple model, rig
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Figure 11.13 - Continuous bag-of-wo
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Figure 11.15 - Reviewing restaurant
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You got that right—arithmetic—r
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There we go, 50 dimensions! It’s
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Equation 11.1 - Embedding arithmeti
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Only 82 out of 50,802 words in the
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Now we can use its encode() method
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Model I — GloVE + ClassifierData
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Pre-trained PyTorch EmbeddingsThe e
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Model Configuration & TrainingLet
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6 self.encoder = encoder7 self.mlp
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Figure 11.20 - Losses—Transformer
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Outputtensor([[[2.6334e-01, 6.9912e
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I want to introduce you to…ELMoBo
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OutputToken: 32 watchThe get_token(
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Helper Function to Retrieve Embeddi
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Output(tensor(-0.5047, device='cuda
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torch.all(new_flair_sentences[0].to
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Outputtensor(0.3504, device='cuda:0
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We can leverage this fact to slight
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We can easily get the embeddings fo
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Figure 11.24 - Losses—simple clas
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We can inspect the pre-trained mode
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Every word piece is prefixed with #
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far, our models used these embeddin
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position_ids = torch.arange(512).ex
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Pre-training TasksMasked Language M
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Then, let’s create an instance of
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If these two sentences were the inp
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The BERT model may take many other
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The contextual word embeddings are
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Model Configuration1 class BERTClas
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"Which BERT is that? DistilBERT?!"D
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Well, you probably don’t want to
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set num_labels=1 as argument.If you
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Output{'attention_mask': [1, 1, 1,
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OutputTrainingArguments(output_dir=
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Method for Computing Accuracy1 def
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loaded_model = (AutoModelForSequenc
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logits.logits.argmax(dim=1)Outputte
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For a complete list of available ta
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[215]. For a demo of GPT-2’s capa
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in Chapter 9, and I reproduce it be
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Data Preparation1 auto_tokenizer =
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Data Preparation1 lm_train_dataset
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The training arguments are roughly
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device_index = (model.device.indexi
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• learning that a language model
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[167] https://huggingface.co/docs/d
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