1.Pytorch保存加载模型

1.1 当提到保存和加载模型时，有三个核心功能需要熟悉：

1.torch.save：将序列化的对象保存到disk。这个函数使用Python的pickle实用程序进行序列化。使用这个函数可以保存各种对象的模型、张量和字典。
2.torch.load：使用pickle unpickle工具将pickle的对象文件反序列化为内存。
3.torch.nn.Module.load_state_dict:使用反序列化状态字典加载model’s参数字典

1.2 保存加载模型2种方式，在保存模型进行推理时，只需要保存训练过的模型的学习参数即可，一个常见的PyTorch约定是使用.pt或.pth文件扩展名保存模型。

第一种：保存和加载整个模型
Save:
torch.save(model_object, 'model.pth')
Load:
model = torch.load('model.pth')
model.eval()

#第二种：仅保存和加载模型参数(推荐使用)
Save：
torch.save(model.state_dict(), 'params.pth')
Load:
model = TheModelClass(*args, **kwargs)
model.load_state_dict(torch.load('params.pth'))
model.eval()
#记住，必须调用model.eval()，以便在运行推断之前将dropout和batch规范化层设置为评估模式。
#如果不这样做，将会产生不一致的推断结果
#在保存用于推理或恢复训练的通用检查点时，必须保存模型的state_dict

注意事项

1、保存模型和加载模型的设备不同

GPU训练的加载到CPU上：

  device = torch.device('cpu')
  model = TheModelClass(*args, **kwargs)
  model.load_state_dict(torch.load(PATH, map_location=device))

CPU训练的加载到GPU上：

  device = torch.device("cuda")
  model = TheModelClass(*args, **kwargs)
  model.load_state_dict(torch.load(PATH, map_location="cuda:0"))  # Choose whatever GPU device number you want
 model.to(device)
  # Make sure to call input = input.to(device) on any input tensors that you feed to the model

2、保存模型和加载模型的设备相同

GPU训练的加载到GPU上：

  device = torch.device("cuda")
  model = TheModelClass(*args, **kwargs)
  model.load_state_dict(torch.load(PATH))
  model.to(device)
  # Make sure to call input = input.to(device) on any input tensors that you feed to the model

2.Pytorch模型转onnx

2.1 如果保存的是整个模型

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

model = torch.load("test.pth") # pytorch模型加载
batch_size = 1  #批处理大小
input_shape = (3, 244, 384)   #输入数据,改成自己的输入shape

# #set the model to inference mode
model.eval()

x = torch.randn(batch_size, *input_shape)   # 生成张量
x = x.to(device)
export_onnx_file = "test.onnx"		# 目的ONNX文件名
torch.onnx.export(model
                    x,
                    export_onnx_file,
                    opset_version=10,
                    do_constant_folding=True,	# 是否执行常量折叠优化
                    input_names=["input"],	# 输入名
                    output_names=["output"],	# 输出名
                    dynamic_axes={
    "input":{
    0:"batch_size"},  # 批处理变量
                                  "output":{
    0:"batch_size"}})

2.2 如果保存的是模型参数

import torch
import torchvision.models as models

torch_model = torch.load("test.pth") # pytorch模型加载

model = models.resnet50() # 模型类实例化，可以是自己的模型
model.fc = torch.nn.Linear(2048, 4)
model.load_state_dict(torch_model) 

batch_size = 1  #批处理大小
input_shape = (3, 244, 384)   #输入数据,改成自己的输入shape

# #set the model to inference mode
model.eval()

x = torch.randn(batch_size, *input_shape)	# 生成张量
export_onnx_file = "test.onnx"			# 目的ONNX文件名
torch.onnx.export(model,
                    x,
                    export_onnx_file,
                    opset_version=10,
                    do_constant_folding=True,	# 是否执行常量折叠优化
                    input_names=["input"],	# 输入名
                    output_names=["output"],	# 输出名
                    dynamic_axes={
    "input":{
    0:"batch_size"},  # 批处理变量
                                  "output":{
    0:"batch_size"}})

3.推理ONNX模型：

1、参考

import os, sys
sys.path.append(os.getcwd())
import onnxruntime
import onnx
import cv2
import torch
import numpy as np
import torchvision.transforms as transforms
 

class ONNXModel():
    def __init__(self, onnx_path):
        """
        :param onnx_path:
        """
        self.onnx_session = onnxruntime.InferenceSession(onnx_path)
        self.input_name = self.get_input_name(self.onnx_session)
        self.output_name = self.get_output_name(self.onnx_session)
        print("input_name:{}".format(self.input_name))
        print("output_name:{}".format(self.output_name))

    def get_output_name(self, onnx_session):
        """
        output_name = onnx_session.get_outputs()[0].name
        :param onnx_session:
        :return:
        """
        output_name = []
        for node in onnx_session.get_outputs():
            output_name.append(node.name)
        return output_name

    def get_input_name(self, onnx_session):
        """
        input_name = onnx_session.get_inputs()[0].name
        :param onnx_session:
        :return:
        """
        input_name = []
        for node in onnx_session.get_inputs():
            input_name.append(node.name)
        return input_name

    def get_input_feed(self, input_name, image_numpy):
        """
        input_feed={self.input_name: image_numpy}
        :param input_name:
        :param image_numpy:
        :return:
        """
        input_feed = {
    }
        for name in input_name:
            input_feed[name] = image_numpy
        return input_feed

    def forward(self, image_numpy):
        '''
        # image_numpy = image.transpose(2, 0, 1)
        # image_numpy = image_numpy[np.newaxis, :]
        # onnx_session.run([output_name], {input_name: x})
        # :param image_numpy:
        # :return:
        '''
        # 输入数据的类型必须与模型一致,以下三种写法都是可以的
        # scores, boxes = self.onnx_session.run(None, {self.input_name: image_numpy})
        # scores, boxes = self.onnx_session.run(self.output_name, input_feed={self.input_name: iimage_numpy})
        input_feed = self.get_input_feed(self.input_name, image_numpy)
        scores, boxes = self.onnx_session.run(self.output_name, input_feed=input_feed)
        return scores, boxes



def to_numpy(tensor):
    return tensor.detach().cpu().numpy() if tensor.requires_grad else tensor.cpu().numpy()

r_model_path="/home/zigangzhao/DMS/mtcnn-pytorch/test0815/onnx_model/rnet.onnx"
o_model_path="/home/zigangzhao/DMS/mtcnn-pytorch/test0815/onnx_model/onet.onnx"


img = cv2.imread("/home/zigangzhao/DMS/mtcnn-pytorch/data_set/train/24/positive/999.jpg")
img = cv2.resize(img, 24, 24), interpolation=cv2.INTER_CUBIC)

"""
# scipy.misc.imread 读取的图片数据是 RGB 格式
# cv2.imread 读取的图片数据是 BGR 格式
# PIL.Image.open 读取的图片数据是RGB格式
# 注意要与pth测试时图片读入格式一致
"""
to_tensor = transforms.ToTensor()
img = to_tensor(img)
img = img.unsqueeze_(0)

------------------------------------------------------------------------------------
方法1：

rnet1 = ONNXModel(r_model_path)
out = rnet1.forward(to_numpy(img))
print(out)
------------------------------------------------------------------------------------
方法2：
rnet_session = onnxruntime.InferenceSession(r_model_path)
onet_session = onnxruntime.InferenceSession(o_model_path)
# compute ONNX Runtime output prediction
inputs = {
    onet_session.get_inputs()[0].name: to_numpy(img)}
outs = onet_session.run(None, inputs)
 
print(outs)

3.2 Resnet18官方模型测试:

import os, sys
sys.path.append(os.getcwd())
import onnxruntime
import onnx
import cv2
import torch
import torchvision.models as models
import numpy as np
import torchvision.transforms as transforms
from PIL import Image

def to_numpy(tensor):
    return tensor.detach().cpu().numpy() if tensor.requires_grad else tensor.cpu().numpy()

def get_test_transform():
    return transforms.Compose([
        transforms.Resize([224, 224]),
        transforms.ToTensor(),
        transforms.Normalize(mean=[0.485, 0.456, 0.406], std=[0.229, 0.224, 0.225]),
    ])

image = Image.open('./images/ILSVRC2012_val_00002557.JPEG') # 289

img = get_test_transform()(image)
img = img.unsqueeze_(0) # -> NCHW, 1,3,224,224
print("input img mean {} and std {}".format(img.mean(), img.std()))

onnx_model_path = "resnet18.onnx"
pth_model_path = "resnet18.pth"

## Host GPU pth测试
resnet18 = models.resnet18()
net = resnet18
net.load_state_dict(torch.load(pth_model_path))
net.eval()
output = net(img)

print("pth weights", output.detach().cpu().numpy())
print("HOST GPU prediction", output.argmax(dim=1)[0].item())

##onnx测试
resnet_session = onnxruntime.InferenceSession(onnx_model_path)
#compute ONNX Runtime output prediction
inputs = {
    resnet_session.get_inputs()[0].name: to_numpy(img)}
outs = resnet_session.run(None, inputs[0])

print("onnx weights", outs)
print("onnx prediction", outs.argmax(axis=1)[0])

参考：https://zhuanlan.zhihu.com/p/159379768