How to load a checkpoint file in a pytorch model?
In my pytorch model, I'm initializing my model and optimizer like this. 

model = MyModelClass(config, shape, x_tr_mean, x_tr,std)
optimizer = optim.SGD(model.parameters(), lr=config.learning_rate)


And here is the path to my checkpoint file. 

checkpoint_file = os.path.join(config.save_dir, "checkpoint.pth")

To load this checkpoint file, I check and see if the checkpoint file exists and then I load it as well as the model and optimizer. 

if os.path.exists(checkpoint_file):
    if config.resume:
        torch.load(checkpoint_file)
        model.load_state_dict(torch.load(checkpoint_file))
        optimizer.load_state_dict(torch.load(checkpoint_file))


Also, here's how I'm saving my model and optimizer. 

 torch.save({'model': model.state_dict(), 'optimizer': optimizer.state_dict(), 'iter_idx': iter_idx, 'best_va_acc': best_va_acc}, checkpoint_file)


For some reason I keep getting a strange error whenever I run this code. 

model.load_state_dict(torch.load(checkpoint_file))
File "/home/Josh/.local/lib/python3.6/site-packages/torch/nn/modules/module.py", line 769, in load_state_dict
self.__class__.__name__, "\n\t".join(error_msgs)))
RuntimeError: Error(s) in loading state_dict for MyModelClass:
        Missing key(s) in state_dict: "mean", "std", "attribute.weight", "attribute.bias".
        Unexpected key(s) in state_dict: "model", "optimizer", "iter_idx", "best_va_acc"


Does anyone know why I'm getting this error? 

You saved the model parameters in a dictionary. You're supposed to use the keys, that you used while saving earlier, to load the model checkpoint and state_dicts like this:

if os.path.exists(checkpoint_file):
    if config.resume:
        checkpoint = torch.load(checkpoint_file)
        model.load_state_dict(checkpoint['model'])
        optimizer.load_state_dict(checkpoint['optimizer'])


You can check the official tutorial on PyTorch website for more info.
