【pytorch】pytorch基础学习

目录

• 1. 前言
• # 2. Deep Learning with PyTorch: A 60 Minute Blitz
  • 2.1 base operations
  • 2.2 train a classifier
• 3 规范化pytorch训练MNIST数据集

1. 前言

  最近在学习pytorch，先照着官方的“60分钟教程”学习了一下，然后再github上找了两个star比较多的项目，自己写了一下，学习一下别人的写法。

# 2. Deep Learning with PyTorch: A 60 Minute Blitz

2.1 base operations

# base operations
import torch

x = torch.empty(5, 3)
print(x)

x = torch.rand(1, 2)
print(x)

x = torch.zeros(4,5, dtype = torch.long)
print(x)

x = torch.tensor([5.5, 3])

print(x)

x = x.new_ones(5, 3, dtype=torch.double)

print(x)

x = torch.randn_like(x, dtype=torch.float)

print(x)
print(x.size())

y = torch.rand(5,3)
print(x+y)

print(torch.add(x, y))

result = torch.empty(5,3)
torch.add(x, y, out=result)
print(result)

result = x + y
print('result = ', result)

result = torch.add(x, y)
print('result2 = ', result)

y.add_(x)
print(y)
# 转置
y.t_()
print(y)
# resize
x = torch.randn(4,4)
y = x.view(16)
z = x.view(-1, 8)
print(x.size(), y.size(), z.size())
print(y)
# 只有一个元素的时候
# If you have a one element tensor, use .item() to get the value as a Python number
x = torch.randn(1)
print(x)
print(x.item())

#  numpy bridge

a = torch.ones(5)
b = a.numpy()
print(a)
print(b)

a.add_(1)
print(a)
print(b)

import numpy as np

a = np.ones(5)
b = torch.from_numpy(a)
np.add(a, 1, out = a)
print(a)
print(b)

# cuda

if torch.cuda.is_available():
    device = torch.device("cuda")
    y = torch.ones_like(x, device=device)
    x = x.to(device)
    z = x + y
    print(z)
    print(z.to("cpu", torch.double))

# Neural Networks
import torch
import torch.nn as nn
import torch.nn.functional as F

class Net(nn.Module):

    def __init__(self):
        # python中的super( test, self).__init__()
        # 首先找到test的父类（比如是类A），然后把类test的对象self转换为类A的对象，然后“被转换”的类A对象调用自己的__init__函数
        super(Net, self).__init__()
        # 1 input image channel, 6 output channels, 5x5 square convolution
        # kernel
        self.conv1 = nn.Conv2d(1, 6, 5)
        self.conv2 = nn.Conv2d(6, 16, 5)
        # an affine operation: y = Wx + b
        self.fc1 = nn.Linear(16*5*5, 120)
        self.fc2 = nn.Linear(120, 84)
        self.fc3 = nn.Linear(84, 10)

    def forward(self, x):
        # Max pooling over a (2, 2) window
        x = F.max_pool2d(F.relu(self.conv1(x)), (2, 2))
        # If the size is a square you can only specify a single number
        x = F.max_pool2d(F.relu(self.conv2(x)), 2)
        x = x.view(-1, self.num_flat_features(x))
        x = F.relu(self.fc1(x))
        x = F.relu(self.fc2(x))
        x = self.fc3(x)
        return x

    def num_flat_features(self, x):
        size = x.size()[1:]  # all dimensions except the batch dimension
        num_features = 1
        for s in size:
            num_features *= s
        return num_features

net = Net()
print(net)

'''
Net(
  (conv1): Conv2d(1, 6, kernel_size=(5, 5), stride=(1, 1))
  (conv2): Conv2d(6, 16, kernel_size=(5, 5), stride=(1, 1))
  (fc1): Linear(in_features=400, out_features=120, bias=True)
  (fc2): Linear(in_features=120, out_features=84, bias=True)
  (fc3): Linear(in_features=84, out_features=10, bias=True)
)
'''

'''
You just have to define the forward function, and the backward function (where gradients are computed) is
 automatically defined for you using autograd. You can use any of the Tensor operations in the forward function. x
 '''

# The learnable parameters of a model are returned by net.parameters()
params = list(net.parameters())
print(len(params))
print(params[0].size())  # conv1's .weight

# output
'''
10
torch.Size([6, 1, 5, 5])
'''
# Let try a random 32x32 input Note: Expected input size to this net(LeNet) is 32x32. To use this net on MNIST dataset, please resize the images from the dataset to 32x32.

input = torch.randn(1, 1, 32, 32)
out = net(input)
print(out)
# Zero the gradient buffers of all parameters and backprops with random gradients:(初始化)
net.zero_grad()
out.backward(torch.randn(1, 10))

'''
torch.nn only supports mini-batches. The entire torch.nn package only supports inputs that are
a mini-batch of samples, and not a single sample.
For example, nn.Conv2d will take in a 4D Tensor of nSamples x nChannels x Height x Width.
If you have a single sample, just use input.unsqueeze(0) to add a fake batch dimension.
'''
# Recap
'''
Recap:
torch.Tensor - A multi-dimensional array with support for autograd operations like backward(). Also holds the gradient w.r.t. the tensor.
nn.Module - Neural network module. Convenient way of encapsulating parameters, with helpers for moving them to GPU, exporting, loading, etc.
nn.Parameter - A kind of Tensor, that is automatically registered as a parameter when assigned as an attribute to a Module.
autograd.Function - Implements forward and backward definitions of an autograd operation. Every Tensor operation, creates at least a single Function node,
that connects to functions that created a Tensor and encodes its history.
'''

output = net(input)
target = torch.randn(10) #a dummy target, for example
target = target.view(1, -1) #  # make it the same shape as output
criterion = nn.MSELoss()

loss = criterion(output, target)
print(loss)
#So, when we call loss.backward(), the whole graph is differentiated w.r.t. the loss,
# and all Tensors in the graph that has requires_grad=True will have their .grad Tensor accumulated with the gradient.

#For illustration, let us follow a few steps backward:
print(loss.grad_fn)  # MSELoss
print(loss.grad_fn.next_functions[0][0])  # Linear
print(loss.grad_fn.next_functions[0][0].next_functions[0][0])  # ReLU

# BACKPROP
# To backpropagate the error all we have to do is to loss.backward(). You need to clear the existing gradients though, else gradients will be accumulated to existing gradients.
# Now we shall call loss.backward(), and have a look at conv1’s bias gradients before and after the backward.
net.zero_grad()     # zeroes the gradient buffers of all parameters

print('conv1.bias.grad before backward')
print(net.conv1.bias.grad)
loss.backward()
print('conv1.bias.grad after backward')
print(net.conv1.bias.grad)

# Observe how gradient buffers had to be manually set to zero using optimizer.zero_grad(). This is because gradients are accumulated as explained in Backprop section.
import torch.optim as optim
# create your optimizer
Optimizer = optim.SGD(net.parameters(), lr= 0.01)
# in your training loop:
Optimizer.zero_grad() # 梯度清零 防止叠加
output = net(input)
loss = criterion(output, target)
loss.backward()
Optimizer.step() ## Does the update

2.2 train a classifier

# 1. load and normalize
import torch
import torchvision
import torchvision.transforms as transforms

# The output of torchvision datasets are PILImage images of range [0, 1]. We transform them to Tensors of normalized range [-1, 1].
# PILImage: python imaging Library ，python平台上图像处理标准库
transform = transforms.Compose([transforms.ToTensor(), transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))]) # 进行Normalize之前必须totensor
trainset = torchvision.datasets.CIFAR10(root = './data', train=True, download=True, transform=transform)
trainloader = torch.utils.data.DataLoader(trainset, batch_size=4, shuffle=True, num_workers=0)

testset = torchvision.datasets.CIFAR10(root='./data', train=False, download=True, transform=transform)
testloader = torch.utils.data.DataLoader(testset, batch_size=4, shuffle=False, num_workers=0)

classes = ('plane', 'car', 'bird', 'cat', 'deer', 'dog', 'frog', 'horse', 'ship','truck')

# show training images
'''
import matplotlib.pyplot as plt
import numpy as np

# functions to show an image

def imshow(img):
    img = img / 2 + 0.5     # unnormalize
    npimg = img.numpy()
    plt.show(np.transpose(npimg, (1, 2, 0)))

# get some random training images
dataiter = iter(trainloader)
images, labels = dataiter.next()

# show images
imshow(torchvision.utils.make_grid(images))
# print labels
print(' '.join('%5s' % classes[labels[j]] for j in range(4)))

'''
# 2.define a foreward network

import torch.nn as nn
import torch.nn.functional as F

class Net(nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        # first, define convolutional filter and weights of fc
        self.conv1 = nn.Conv2d(3, 6, 5)
        self.conv2 = nn.Conv2d(6, 16, 5)
        self.max_pool = nn.MaxPool2d(2,2)
        self.fc1 = nn.Linear(16*5*5, 120)
        self.fc2 = nn.Linear(120, 84)
        self.fc3 = nn.Linear(84, 10)

    def forward(self, x):
        x = F.relu(self.conv1(x))
        x = self.max_pool(x)
        x = F.relu(self.conv2(x))
        x = self.max_pool(x)
        x = x.view(-1, 16*5*5)
        x = F.relu(self.fc1(x))
        x = F.relu(self.fc2(x))
        x = self.fc3(x)
        return x

net = Net()

# 3. choose a optimizer
import torch.optim as optim

criterion = nn.CrossEntropyLoss() # loss
optimizer = optim.SGD(net.parameters(),lr=0.001,momentum=0.9)

# 4. train the network

for epoch in range(2): # loop over the whole dataset multiple times
    total_loss = 0
    for i, data in enumerate(trainloader, 0): # start from 0
        optimizer.zero_grad() # clean the gradient every batch
        inputs, labels = data  # get a batch data
        outputs = net(inputs) # get the outputs
        loss = criterion(outputs, labels) # get the constant loss
        loss.backward() # compute every parameter's gradient
        optimizer.step() # update the parameter
        total_loss += loss.item()

        # print the information
        if i % 2000 == 1999: # print the loss every 2000 mini-batches
            print('[%d %5d] loss: %.3f' % (epoch+1, i+1, total_loss / 2000))
            total_loss = 0

print('Finished Training')

# 5.test the network on the test data
'''
dataiter = iter(testloader)
images, labels = dataiter.next()

# print images
imshow(torchvision.utils.make_grid(images))
print('GroundTruth: ', ' '.join('%5s' % classes[labels[j]] for j in range(4)))

outputs = net(images)
'''
# get the accurate

total = 0
correct = 0
with torch.no_grad():
    for data in testloader:
        images, labels = data
        outputs = net(images)
        _, prediction = torch.max(outputs.data, 1) #torch.max(a,1/0) 返回每一行/列中最大值的那个元素，且返回其索引（返回最大元素在这一行的列索引）,_用来获取值，但没用
        # outputs.data 应该是获取 tensor
        total += labels.size(0)
        correct += (prediction == labels).sum().item()

print('Accuracy of the network on the 10000 test images: %d %%' % (100 * correct / total))

# get the class_accurate
class_correct = list(0. for i in range(10))  # create a list for 10 class
class_total = list(0. for i in range(10))

with torch.no_grad():
    for data in testloader:
        images, labels = data
        outputs = net(images)
        _, prediction = torch.max(outputs, 1)
        c = (prediction == labels).squeeze() # get a list of series class
        for i in range(4): # 4 is batch_size
            label = labels[i]
            class_correct[label] += c[i].item()
            class_total[label] += 1

for i in range(10):
    print('Accuracy of %5s : %2d %%' % (classes[i], 100 * class_correct[i] / class_total[i]))

# train on single GPU
device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")
# Assume that we are on a CUDA machine, then this should print a CUDA device:
print(device)
net.to(device)
inputs, labels = inputs.to(device), labels.to(device)

# train on multiple GPU
'''
DataParallel splits your data automatically and sends job orders to multiple models on several GPUs. After
each model finishes their job, DataParallel collects and merges the results before returning it to you.
'''

import torch
import torch.nn as nn
from torch.utils.data import Dataset, DataLoader

# Parameters and DataLoaders
input_size = 5
output_size = 2

batch_size = 30
data_size = 100

device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")

# dummy dataset
class RandomDataset(Dataset):

    def __init__(self, size, length):
        self.len = length
        self.data = torch.randn(length, size)

    def __getitem__(self, index):
        return self.data[index]

    def __len__(self):
        return self.len

rand_loader = DataLoader(dataset=RandomDataset(input_size, data_size),
                         batch_size=batch_size, shuffle=True)

class Model(nn.Module):
    # Our model

    def __init__(self, input_size, output_size):
        super(Model, self).__init__()
        self.fc = nn.Linear(input_size, output_size)

    def forward(self, input):
        output = self.fc(input)
        print("\tIn Model: input size", input.size(),
              "output size", output.size())

        return output

model = Model(input_size, output_size)
if torch.cuda.device_count() > 1:
  print("Let's use", torch.cuda.device_count(), "GPUs!")
  # dim = 0 [30, xxx] -> [10, ...], [10, ...], [10, ...] on 3 GPUs
  model = nn.DataParallel(model)

model.to(device)

for data in rand_loader:
    input = data.to(device)
    output = model(input)
    print("Outside: input size", input.size(),
          "output_size", output.size())
'''
If you have 2, you will see:
# on 2 GPUs
Let's use 2 GPUs!
    In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
    In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
    In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
    In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
    In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
    In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
    In Model: input size torch.Size([5, 5]) output size torch.Size([5, 2])
    In Model: input size torch.Size([5, 5]) output size torch.Size([5, 2])
Outside: input size torch.Size([10, 5]) output_size torch.Size([10, 2])
'''

'''If you have 3 GPUs, you will see:

Let's use 3 GPUs!
    In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2])
    In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2])
    In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
    In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2])
    In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2])
    In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
    In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2])
    In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2])
    In Model: input size torch.Size([10, 5]) output size torch.Size([10, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2])
Outside: input size torch.Size([10, 5]) output_size torch.Size([10, 2])'''

'''If you have 8, you will see:

Let's use 8 GPUs!
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([4, 5]) output size torch.Size([4, 2])
    In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2])
Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2])
    In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2])
    In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2])
    In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2])
    In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2])
    In Model: input size torch.Size([2, 5]) output size torch.Size([2, 2])
Outside: input size torch.Size([10, 5]) output_size torch.Size([10, 2])'''

3 规范化pytorch训练MNIST数据集

import torch
import torch.nn as nn
import torch.optim as optim
import torch.nn.functional as F
import torchvision
from torchvision import datasets, transforms
import argparse

class Net(nn.Module):

    def __init__(self):
        super(Net, self).__init__()
        self.conv1 = nn.Conv2d(1, 10, 5)
        self.conv2 = nn.Conv2d(10, 20, 5)
        self.conv2_dropout = nn.Dropout2d()
        self.max_pool = nn.MaxPool2d(2, 2)
        self.fc1 = nn.Linear(320, 50)
        self.fc2 = nn.Linear(50, 10)

    def forward(self, x):
        x = F.relu(self.max_pool(self.conv1(x)))
        x = F.relu(self.max_pool(self.conv2_dropout(self.conv2(x)))) # dropout need before relu operation
        x = x.view(-1, 320)
        # print(x.size())
        x = F.relu(self.fc1(x))
        x = F.dropout(x, training=self.training)
        x = self.fc2(x)
        return F.log_softmax(x, dim=1)  # dim 代表纬度， 加了softmax， 相当于返回就是一个概率

def train(args, model, device, train_loader, optimizer, epoch):
    model.train() # 当有drop跟nolizition等操作的时候，需要加上这一句
    for i, data in enumerate(train_loader):
        images, labels = data
        images = images.to(device)
        labels = labels.to(device)
        optimizer.zero_grad()
        outputs = model(images)
        loss = F.nll_loss(outputs, labels)  # loss = F.nll_loss()
        loss.backward()
        optimizer.step()
        # get the information
        if i % args.log_interval == 0:
            print('Train Epoch: {} [{}/{} ({:.0f}%)]\tLoss: {:.6f}'.format(
                epoch, i * len(images), len(train_loader.dataset),
                       100. * i / len(train_loader), loss.item())) # 这里没有取log_interval个sample的loss的平均，即某一个log_interval的loss

def test(args, model, device, test_loader):
    model.eval()
    correct_num = 0
    test_loss = 0.
    with torch.no_grad():
        for images, labels in test_loader:
            images = images.to(device)
            labels = labels.to(device)
            outputs = model(images)
            _, prediction = torch.max(outputs.data, 1) # prediction里面是一维索引
            correct_num += (prediction == labels).sum().item() # 获得一个batch正确的数量
            test_loss += F.nll_loss(outputs, labels, reduction='sum').item()   # sum up batch loss

    total_num = len(test_loader.dataset)
    print('\nTest set: Average loss: {:.4f}, Accuracy: {}/{} ({:.0f}%)\n'.format(
        test_loss / total_num, correct_num, total_num,
        100. * correct_num / total_num))

def main():
    parser = argparse.ArgumentParser(description='PyTorch MNIST')
    parser.add_argument('--batch-size', type=int, default=64, metavar='M',
                        help='input batch size for training (default: 64)')
    parser.add_argument('--test_batch-size', type=int, default=1000, metavar='N',
                        help='input batch size for testing (default: 1000)')
    parser.add_argument('--epochs', type=int, default=10, metavar='N',
                        help='number of epochs to train (default: 10)')
    parser.add_argument('--lr', type=float, default=0.01, metavar='LR',
                        help='learning rate (default: 0.01)')
    parser.add_argument('--momentum', type=float, default=0.5, metavar='M',
                        help='SGD momentum (default: 0.5)')
    parser.add_argument('--no-cuda', action='store_true', default=False,
                        help='disables CUDA training')
    parser.add_argument('--seed', type=int, default=1, metavar='S',
                        help='random seed (default: 1)')
    parser.add_argument('--log-interval', type=int, default=10, metavar='N',
                        help='how many batches to wait before logging training status')
    args = parser.parse_args()

    use_cuda = not args.no_cuda and torch.cuda.is_available()

    torch.manual_seed(args.seed)

    device = torch.device("cuda" if use_cuda else "cpu")

    kwargs = {'num_workers': 1, 'pin_memory': True} if use_cuda else {}
    train_loader = torch.utils.data.DataLoader(
        datasets.MNIST('../data', train=True, download=True,
                       transform=transforms.Compose([
                           transforms.ToTensor(),
                           transforms.Normalize((0.1307,), (0.3081,))
                       ])),
        batch_size=args.batch_size, shuffle=True, **kwargs)
    test_loader = torch.utils.data.DataLoader(
        datasets.MNIST('../data', train=False, transform=transforms.Compose([
            transforms.ToTensor(),
            transforms.Normalize((0.1307,), (0.3081,))
        ])),
        batch_size=args.test_batch_size, shuffle=True, **kwargs)

    model = Net().to(device)
    optimizer = optim.SGD(model.parameters(), lr=args.lr, momentum=args.momentum)

    for epoch in range(1, args.epochs + 1):
        train(args, model, device, train_loader, optimizer, epoch)
        test(args, model, device, test_loader)

if __name__ == '__main__':
    main()