Pytorch模型迁移和迁移学习

1. 利用resnet18做迁移学习

import torch
from torchvision import models

if __name__ == "__main__":
    # device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
    device = 'cpu'
    print("-----device:{}".format(device))
    print("-----Pytorch version:{}".format(torch.__version__))

    input_tensor = torch.zeros(1, 3, 100, 100)
    print('input_tensor:', input_tensor.shape)
    pretrained_file = "model/resnet18-5c106cde.pth"
    model = models.resnet18()
    model.load_state_dict(torch.load(pretrained_file))
    model.eval()
    out = model(input_tensor)
    print("out:", out.shape, out[0, 0:10])

结果输出:

input_tensor: torch.Size([1, 3, 100, 100])
out: torch.Size([1, 1000]) tensor([ 0.4010, 0.8436, 0.3072, 0.0627, 0.4446, 0.8470, 0.1882, 0.7012,0.2988, -0.7574], grad_fn=<SliceBackward>)

如果,我们修改了resnet18的网络结构,如何将原来预训练模型参数(resnet18-5c106cde.pth)迁移到新的resnet18网络中呢?

比如,这里将官方的resnet18的self.layer4 = self._make_layer(block, 512, layers[3], stride=2)改为:self.layer44 = self._make_layer(block, 512, layers[3], stride=2)

class ResNet(nn.Module):

    def __init__(self, block, layers, num_classes=1000, zero_init_residual=False):
        super(ResNet, self).__init__()
        self.inplanes = 64
        self.conv1 = nn.Conv2d(3, 64, kernel_size=7, stride=2, padding=3,
                               bias=False)
        self.bn1 = nn.BatchNorm2d(64)
        self.relu = nn.ReLU(inplace=True)
        self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)
        self.layer1 = self._make_layer(block, 64, layers[0])
        self.layer2 = self._make_layer(block, 128, layers[1], stride=2)
        self.layer3 = self._make_layer(block, 256, layers[2], stride=2)
        self.layer44 = self._make_layer(block, 512, layers[3], stride=2)
        self.avgpool = nn.AdaptiveAvgPool2d((1, 1))
        self.fc = nn.Linear(512 * block.expansion, num_classes)

        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                nn.init.kaiming_normal_(m.weight, mode='fan_out', nonlinearity='relu')
            elif isinstance(m, nn.BatchNorm2d):
                nn.init.constant_(m.weight, 1)
                nn.init.constant_(m.bias, 0)

        # Zero-initialize the last BN in each residual branch,
        # so that the residual branch starts with zeros, and each residual block behaves like an identity.
        # This improves the model by 0.2~0.3% according to https://arxiv.org/abs/1706.02677
        if zero_init_residual:
            for m in self.modules():
                if isinstance(m, Bottleneck):
                    nn.init.constant_(m.bn3.weight, 0)
                elif isinstance(m, BasicBlock):
                    nn.init.constant_(m.bn2.weight, 0)

    def _make_layer(self, block, planes, blocks, stride=1):
        downsample = None
        if stride != 1 or self.inplanes != planes * block.expansion:
            downsample = nn.Sequential(
                conv1x1(self.inplanes, planes * block.expansion, stride),
                nn.BatchNorm2d(planes * block.expansion),
            )

        layers = []
        layers.append(block(self.inplanes, planes, stride, downsample))
        self.inplanes = planes * block.expansion
        for _ in range(1, blocks):
            layers.append(block(self.inplanes, planes))

        return nn.Sequential(*layers)

    def forward(self, x):
        x = self.conv1(x)
        x = self.bn1(x)
        x = self.relu(x)
        x = self.maxpool(x)

        x = self.layer1(x)
        x = self.layer2(x)
        x = self.layer3(x)
        x = self.layer44(x)

        x = self.avgpool(x)
        x = x.view(x.size(0), -1)
        x = self.fc(x)

        return x

这时,直接加载模型:

model = models.resnet18()
model.load_state_dict(torch.load(pretrained_file))

这时,肯定会报错,类似:Missing key(s) in state_dict或者Unexpected key(s) in state_dict的错误:

RuntimeError: Error(s) in loading state_dict for ResNet:
Missing key(s) in state_dict: "layer44.0.conv1.weight", "layer44.0.bn1.weight", "layer44.0.bn1.bias", "layer44.0.bn1.running_mean", "layer44.0.bn1.running_var", "layer44.0.conv2.weight", "layer44.0.bn2.weight", "layer44.0.bn2.bias", "layer44.0.bn2.running_mean", "layer44.0.bn2.running_var", "layer44.0.downsample.0.weight", "layer44.0.downsample.1.weight", "layer44.0.downsample.1.bias", "layer44.0.downsample.1.running_mean", "layer44.0.downsample.1.running_var", "layer44.1.conv1.weight", "layer44.1.bn1.weight", "layer44.1.bn1.bias", "layer44.1.bn1.running_mean", "layer44.1.bn1.running_var", "layer44.1.conv2.weight", "layer44.1.bn2.weight", "layer44.1.bn2.bias", "layer44.1.bn2.running_mean", "layer44.1.bn2.running_var".
Unexpected key(s) in state_dict: "layer4.0.conv1.weight", "layer4.0.bn1.running_mean", "layer4.0.bn1.running_var", "layer4.0.bn1.weight", "layer4.0.bn1.bias", "layer4.0.conv2.weight", "layer4.0.bn2.running_mean", "layer4.0.bn2.running_var", "layer4.0.bn2.weight", "layer4.0.bn2.bias", "layer4.0.downsample.0.weight", "layer4.0.downsample.1.running_mean", "layer4.0.downsample.1.running_var", "layer4.0.downsample.1.weight", "layer4.0.downsample.1.bias", "layer4.1.conv1.weight", "layer4.1.bn1.running_mean", "layer4.1.bn1.running_var", "layer4.1.bn1.weight", "layer4.1.bn1.bias", "layer4.1.conv2.weight", "layer4.1.bn2.running_mean", "layer4.1.bn2.running_var", "layer4.1.bn2.weight", "layer4.1.bn2.bias".

Process finished with

RuntimeError: Error(s) in loading state_dict for ResNet:
Unexpected key(s) in state_dict: "layer4.0.conv1.weight", "layer4.0.bn1.running_mean", "layer4.0.bn1.running_var", "layer4.0.bn1.weight", "layer4.0.bn1.bias", "layer4.0.conv2.weight", "layer4.0.bn2.running_mean", "layer4.0.bn2.running_var", "layer4.0.bn2.weight", "layer4.0.bn2.bias", "layer4.0.downsample.0.weight", "layer4.0.downsample.1.running_mean", "layer4.0.downsample.1.running_var", "layer4.0.downsample.1.weight", "layer4.0.downsample.1.bias", "layer4.1.conv1.weight", "layer4.1.bn1.running_mean", "layer4.1.bn1.running_var", "layer4.1.bn1.weight", "layer4.1.bn1.bias", "layer4.1.conv2.weight", "layer4.1.bn2.running_mean", "layer4.1.bn2.running_var", "layer4.1.bn2.weight", "layer4.1.bn2.bias".

我们希望将原来预训练模型参数(resnet18-5c106cde.pth)迁移到新的resnet18网络,当然只能迁移二者相同的模型参数,不同的参数还是随机初始化的.



def transfer_model(pretrained_file, model):
    '''
    只导入pretrained_file部分模型参数
    tensor([-0.7119,  0.0688, -1.7247, -1.7182, -1.2161, -0.7323, -2.1065, -0.5433,-1.5893, -0.5562]
    update:
        D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
        If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]
        If E is present and lacks a .keys() method, then does:  for k, v in E: D[k] = v
        In either case, this is followed by: for k in F:  D[k] = F[k]
    :param pretrained_file:
    :param model:
    :return:
    '''
    pretrained_dict = torch.load(pretrained_file)  # get pretrained dict
    model_dict = model.state_dict()  # get model dict
    # 在合并前(update),需要去除pretrained_dict一些不需要的参数
    pretrained_dict = transfer_state_dict(pretrained_dict, model_dict)
    model_dict.update(pretrained_dict)  # 更新(合并)模型的参数
    model.load_state_dict(model_dict)
    return model


def transfer_state_dict(pretrained_dict, model_dict):
    '''
    根据model_dict,去除pretrained_dict一些不需要的参数,以便迁移到新的网络
    url: https://blog.csdn.net/qq_34914551/article/details/87871134
    :param pretrained_dict:
    :param model_dict:
    :return:
    '''
    # state_dict2 = {k: v for k, v in save_model.items() if k in model_dict.keys()}
    state_dict = {}
    for k, v in pretrained_dict.items():
        if k in model_dict.keys():
            # state_dict.setdefault(k, v)
            state_dict[k] = v
        else:
            print("Missing key(s) in state_dict :{}".format(k))
    return state_dict


if __name__ == "__main__":

    input_tensor = torch.zeros(1, 3, 100, 100)
    print('input_tensor:', input_tensor.shape)
    pretrained_file = "model/resnet18-5c106cde.pth"
    # model = resnet18()
    # model.load_state_dict(torch.load(pretrained_file))
    # model.eval()
    # out = model(input_tensor)
    # print("out:", out.shape, out[0, 0:10])

    model1 = resnet18()
    model1 = transfer_model(pretrained_file, model1)
    out1 = model1(input_tensor)
    print("out1:", out1.shape, out1[0, 0:10])

2. 修改网络名称并迁移学习

上面的例子,只是将官方的resnet18的self.layer4 = self._make_layer(block, 512, layers[3], stride=2)改为了:self.layer44 = self._make_layer(block, 512, layers[3], stride=2),我们仅仅是修改了一个网络名称而已,就导致 model.load_state_dict(torch.load(pretrained_file))出错,

那么,我们如何将预训练模型"model/resnet18-5c106cde.pth"转换成符合新的网络的模型参数呢?

方法很简单,只需要将resnet18-5c106cde.pth的模型参数中所有前缀为layer4的名称,改为layer44即可

本人已经定义好了方法:

modify_state_dict(pretrained_dict, model_dict, old_prefix, new_prefix)

def string_rename(old_string, new_string, start, end):
    new_string = old_string[:start] + new_string + old_string[end:]
    return new_string


def modify_model(pretrained_file, model, old_prefix, new_prefix):
    '''
    :param pretrained_file:
    :param model:
    :param old_prefix:
    :param new_prefix:
    :return:
    '''
    pretrained_dict = torch.load(pretrained_file)
    model_dict = model.state_dict()
    state_dict = modify_state_dict(pretrained_dict, model_dict, old_prefix, new_prefix)
    model.load_state_dict(state_dict)
    return model


def modify_state_dict(pretrained_dict, model_dict, old_prefix, new_prefix):
    '''
    修改model dict
    :param pretrained_dict:
    :param model_dict:
    :param old_prefix:
    :param new_prefix:
    :return:
    '''
    state_dict = {}
    for k, v in pretrained_dict.items():
        if k in model_dict.keys():
            # state_dict.setdefault(k, v)
            state_dict[k] = v
        else:
            for o, n in zip(old_prefix, new_prefix):
                prefix = k[:len(o)]
                if prefix == o:
                    kk = string_rename(old_string=k, new_string=n, start=0, end=len(o))
                    print("rename layer modules:{}-->{}".format(k, kk))
                    state_dict[kk] = v
    return state_dict

if __name__ == "__main__":
    input_tensor = torch.zeros(1, 3, 100, 100)
    print('input_tensor:', input_tensor.shape)
    pretrained_file = "model/resnet18-5c106cde.pth"
    # model = models.resnet18()
    # model.load_state_dict(torch.load(pretrained_file))
    # model.eval()
    # out = model(input_tensor)
    # print("out:", out.shape, out[0, 0:10])
    #
    # model1 = resnet18()
    # model1 = transfer_model(pretrained_file, model1)
    # out1 = model1(input_tensor)
    # print("out1:", out1.shape, out1[0, 0:10])
    #
    new_file = "new_model.pth"
    model = resnet18()
    new_model = modify_model(pretrained_file, model, old_prefix=["layer4"], new_prefix=["layer44"])
    torch.save(new_model.state_dict(), new_file)

    model2 = resnet18()
    model2.load_state_dict(torch.load(new_file))
    model2.eval()
    out2 = model2(input_tensor)
    print("out2:", out2.shape, out2[0, 0:10])

这时,输出,跟之前一模一样了

out: torch.Size([1, 1000]) tensor([ 0.4010, 0.8436, 0.3072, 0.0627, 0.4446, 0.8470, 0.1882, 0.7012,0.2988, -0.7574], grad_fn=<SliceBackward>)

3.去除原模型的某些模块

下面是在不修改原模型代码的情况下,通过"resnet18.named_children()"和"resnet18.children()"的方法去除子模块"fc"和"avgpool"

import torch
import torchvision.models as models
from collections import OrderedDict

if __name__=="__main__":
    resnet18 = models.resnet18(False)
    print("resnet18",resnet18)

    # use named_children()
    resnet18_v1 = OrderedDict(resnet18.named_children())
    # remove avgpool,fc
    resnet18_v1.pop("avgpool")
    resnet18_v1.pop("fc")
    resnet18_v1 = torch.nn.Sequential(resnet18_v1)
    print("resnet18_v1",resnet18_v1)
    # use children
    resnet18_v2 = torch.nn.Sequential(*list(resnet18.children())[:-2])
    print(resnet18_v2,resnet18_v2)

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