上一篇文章中已经通过将dsets.py实现将数据集封装加载，之后就可以通过建立了模型并编写training脚本实现模型的训练了。这一篇文章主要是对《pytorch深度学习实战》第11章内容做的笔记。
一、目标
1、建立简单的卷积神经网络
2、编写训练函数
3、编写训练日志（训练和验证过程的loss，accuracy等）数据结构
4、使用tensorboard可视化训练信息。
二、要点说明
1. 对函数使用通用的系统进程级别的调用
原书代码的【code/p2_run_everything.ipynb】的cell2中，定义了一个通用的系统进程方式的调用方法。通过这种方法可以调用所有脚本中的函数。但个人认为还是挺麻烦的，一点都不人性化。
def run(app, *argv):
argv = list(argv)
argv.insert(0, '--num-workers=4') # <1> 使用4个核
log.info("Running: {}({!r}).main()".format(app, argv))
app_cls = importstr(*app.rsplit('.', 1)) # <2> # 动态加载库
app_cls(argv).main() # 调用app类的main函数
log.info("Finished: {}.{!r}).main()".format(app, argv))使用示例：从p2ch11文件夹的training.py文件中importLunaTrainingApp类并调用其main函数，函数的输入参数是epochs=1。
run('p2ch11.training.LunaTrainingApp', '--epochs=1')其中：
1.1 importstr函数
函数是为了实现动态调用各个库和库函数。类似于from 【pkg_name】 import 【func_name】的作用。通过importstr可以实现动态加载函数，而不用调用前用import声明。
1.2 rsplit函数
函数用法：list = str.rsplit(sep, maxsplit)。可参考下面的文章。简单而言就是对字符【str】按照【sep】分隔符进行拆分，从字符右侧开始拆分，一共拆分【maxsplit】次。返回的是拆分结果是一个list。
Python实用语法之rsplit_明 总 有的博客-CSDN博客_python rsplit
2. 模型建立
书中在11章用的是简单的卷积堆叠+线性层的神经网络结果，没任何特别之处。其中线性层由于只是简单2分类（结节是否为肿瘤），所以只用了一个线性层。卷积和池化用的是3维的卷积和池化。
2.1 多GPU设置
多GPU训练可通过nn.DataParallel(model)或DistributedParallel函数实现，前者较为简单，一般用在单机多卡场景，后者配置较为复杂，一般用在多台计算机的多卡场景。
2.2 优化器
一般开始训练时可以先尝试使用带动量的SGD，lr=0.001，momentum=0.9，不行再换其他优化器，如Adam。
2.3 模型输入尺寸
在上一篇文章中的ct类介绍中，width_irc参数定义了每个在irc坐标系的尺寸大小。也是数据集输入到模型的input_size。
2.4 模型信息
使用torchinfo库或者torchsummary库的summary函数都可以打印模型的参数信息。具体方法如下：
from p2ch11.model import LunaModel
import torchinfo # 安装命令conda install torchinfo
model = LunaModel()
torchinfo.summary(model, (1, 32, 48, 48), batch_dim=0,
col_names = ('input_size', 'output_size', 'num_params', 'kernel_size', 'mult_adds'), verbose = 1)运行结果，即模型信息如下：
=====================================================================================================================================================================
Layer (type:depth-idx) Input Shape Output Shape Param # Kernel Shape Mult-Adds
=====================================================================================================================================================================
LunaModel [1, 1, 32, 48, 48] [1, 2] -- -- --
├─BatchNorm3d: 1-1 [1, 1, 32, 48, 48] [1, 1, 32, 48, 48] 2 -- 2
├─LunaBlock: 1-2 [1, 1, 32, 48, 48] [1, 8, 16, 24, 24] -- -- --
│ └─Conv3d: 2-1 [1, 1, 32, 48, 48] [1, 8, 32, 48, 48] 224 [3, 3, 3] 16,515,072
│ └─ReLU: 2-2 [1, 8, 32, 48, 48] [1, 8, 32, 48, 48] -- -- --
│ └─Conv3d: 2-3 [1, 8, 32, 48, 48] [1, 8, 32, 48, 48] 1,736 [3, 3, 3] 127,991,808
│ └─ReLU: 2-4 [1, 8, 32, 48, 48] [1, 8, 32, 48, 48] -- -- --
│ └─MaxPool3d: 2-5 [1, 8, 32, 48, 48] [1, 8, 16, 24, 24] -- 2 --
├─LunaBlock: 1-3 [1, 8, 16, 24, 24] [1, 16, 8, 12, 12] -- -- --
│ └─Conv3d: 2-6 [1, 8, 16, 24, 24] [1, 16, 16, 24, 24] 3,472 [3, 3, 3] 31,997,952
│ └─ReLU: 2-7 [1, 16, 16, 24, 24] [1, 16, 16, 24, 24] -- -- --
│ └─Conv3d: 2-8 [1, 16, 16, 24, 24] [1, 16, 16, 24, 24] 6,928 [3, 3, 3] 63,848,448
│ └─ReLU: 2-9 [1, 16, 16, 24, 24] [1, 16, 16, 24, 24] -- -- --
│ └─MaxPool3d: 2-10 [1, 16, 16, 24, 24] [1, 16, 8, 12, 12] -- 2 --
├─LunaBlock: 1-4 [1, 16, 8, 12, 12] [1, 32, 4, 6, 6] -- -- --
│ └─Conv3d: 2-11 [1, 16, 8, 12, 12] [1, 32, 8, 12, 12] 13,856 [3, 3, 3] 15,962,112
│ └─ReLU: 2-12 [1, 32, 8, 12, 12] [1, 32, 8, 12, 12] -- -- --
│ └─Conv3d: 2-13 [1, 32, 8, 12, 12] [1, 32, 8, 12, 12] 27,680 [3, 3, 3] 31,887,360
│ └─ReLU: 2-14 [1, 32, 8, 12, 12] [1, 32, 8, 12, 12] -- -- --
│ └─MaxPool3d: 2-15 [1, 32, 8, 12, 12] [1, 32, 4, 6, 6] -- 2 --
├─LunaBlock: 1-5 [1, 32, 4, 6, 6] [1, 64, 2, 3, 3] -- -- --
│ └─Conv3d: 2-16 [1, 32, 4, 6, 6] [1, 64, 4, 6, 6] 55,360 [3, 3, 3] 7,971,840
│ └─ReLU: 2-17 [1, 64, 4, 6, 6] [1, 64, 4, 6, 6] -- -- --
│ └─Conv3d: 2-18 [1, 64, 4, 6, 6] [1, 64, 4, 6, 6] 110,656 [3, 3, 3] 15,934,464
│ └─ReLU: 2-19 [1, 64, 4, 6, 6] [1, 64, 4, 6, 6] -- -- --
│ └─MaxPool3d: 2-20 [1, 64, 4, 6, 6] [1, 64, 2, 3, 3] -- 2 --
├─Linear: 1-6 [1, 1152] [1, 2] 2,306 -- 2,306
├─Softmax: 1-7 [1, 2] [1, 2] -- -- --
=====================================================================================================================================================================
Total params: 222,220
Trainable params: 222,220
Non-trainable params: 0
Total mult-adds (M): 312.11
=====================================================================================================================================================================
Input size (MB): 0.29
Forward/backward pass size (MB): 13.12
Params size (MB): 0.89
Estimated Total Size (MB): 14.31
=====================================================================================================================================================================
Process finished with exit code 0
3. 初始化
训练开始前，需要对权重进行初始化，初始化方法是通用的，具体参照书中代码【model.py】的_init_weights函数。
def _init_weights(self):
for m in self.modules():
if type(m) in {
nn.Linear,
nn.Conv3d,
nn.Conv2d,
nn.ConvTranspose2d,
nn.ConvTranspose3d,
}:
nn.init.kaiming_normal_(
m.weight.data, a=0, mode='fan_out', nonlinearity='relu',
)
if m.bias is not None:
fan_in, fan_out = \
nn.init._calculate_fan_in_and_fan_out(m.weight.data)
bound = 1 / math.sqrt(fan_out)
nn.init.normal_(m.bias, -bound, bound)三、关键函数
关键函数不多，基本都是torch的内置函数，剩下的都是一些方便查看训练结果的日志功能的函数。具体还是得看代码。
代码
1. 网络模型 model.py
代码如下：
import math
from torch import nn as nn
from util.logconf import logging
log = logging.getLogger(__name__)
# log.setLevel(logging.WARN)
# log.setLevel(logging.INFO)
log.setLevel(logging.DEBUG)
class LunaModel(nn.Module):
def __init__(self, in_channels=1, conv_channels=8):
super().__init__()
self.tail_batchnorm = nn.BatchNorm3d(1)
self.block1 = LunaBlock(in_channels, conv_channels)
self.block2 = LunaBlock(conv_channels, conv_channels * 2)
self.block3 = LunaBlock(conv_channels * 2, conv_channels * 4)
self.block4 = LunaBlock(conv_channels * 4, conv_channels * 8)
self.head_linear = nn.Linear(1152, 2)
self.head_softmax = nn.Softmax(dim=1)
self._init_weights()
# see also https://github.com/pytorch/pytorch/issues/18182
def _init_weights(self):
for m in self.modules():
if type(m) in {
nn.Linear,
nn.Conv3d,
nn.Conv2d,
nn.ConvTranspose2d,
nn.ConvTranspose3d,
}:
nn.init.kaiming_normal_(
m.weight.data, a=0, mode='fan_out', nonlinearity='relu',
)
if m.bias is not None:
fan_in, fan_out = \
nn.init._calculate_fan_in_and_fan_out(m.weight.data)
bound = 1 / math.sqrt(fan_out)
nn.init.normal_(m.bias, -bound, bound)
def forward(self, input_batch):
bn_output = self.tail_batchnorm(input_batch)
block_out = self.block1(bn_output)
block_out = self.block2(block_out)
block_out = self.block3(block_out)
block_out = self.block4(block_out)
conv_flat = block_out.view(
block_out.size(0),
-1,
)
linear_output = self.head_linear(conv_flat)
return linear_output, self.head_softmax(linear_output)
class LunaBlock(nn.Module):
def __init__(self, in_channels, conv_channels):
super().__init__()
self.conv1 = nn.Conv3d(
in_channels, conv_channels, kernel_size=3, padding=1, bias=True,
)
self.relu1 = nn.ReLU(inplace=True)
self.conv2 = nn.Conv3d(
conv_channels, conv_channels, kernel_size=3, padding=1, bias=True,
)
self.relu2 = nn.ReLU(inplace=True)
self.maxpool = nn.MaxPool3d(2, 2)
def forward(self, input_batch):
block_out = self.conv1(input_batch)
block_out = self.relu1(block_out)
block_out = self.conv2(block_out)
block_out = self.relu2(block_out)
return self.maxpool(block_out)
后续再继续写