I use this to load the pretrained weights:
resnet50_weights = torch.load("resnet50-19c8e357.pth")
so
model_resnet.load_state_dict(resnet50_weights.state_dict())

would raise error:
'collections.OrderedDict' object has no attribute 'state_dict'

As for    Do you really need to manually load each parameter and buffer?
Actually no, I am new to pytorch is there’s a better way to do what I want ,I would always prefer it! But for curiosity sake ,I still wonder why  it fails…