APIs to import weights from external frameworks.

[david-berthelot]

Demonstrated on PyTorch VGG.

The core function is objax.util.convert.import_weights:

• It takes a variable collection target_vc (basically the model variables for which to set the weights).
• Then source_numpy is a dictionary of numpy values and their names (in a possibly different naming convention than Objax', say for example PyTorch).
• source_names maps objax names to the source_numpy names, so that from a variable we can find the numpy value to set its weight.
• numpy_convert is a dictionary that maps module variables names to actions (functions). The actions are used to perform conversions (like transpositions or reshaping for example). Here are some examples:

ARRAY_CONVERT = {
    '(BatchNorm2D).beta': assign,
    '(BatchNorm2D).gamma': assign,
    '(BatchNorm2D).running_mean': assign,
    '(BatchNorm2D).running_var': assign,
    '(Conv2D).b': assign,
    '(Conv2D).w': lambda x, y: assign(x, y.transpose((2, 3, 1, 0))),
    '(Linear).b': assign,
    '(Linear).w': lambda x, y: assign(x, y.T),
}

[kihyuks]

LGTM.

1. One minor comment on the folder and file names:
   vgg_pytorch/pytorch_vgg.py --> maybe better to make them consistent?

2. no separate test example?

[david-berthelot]

LGTM.

1. One minor comment on the folder and file names:
   vgg_pytorch/pytorch_vgg.py --> maybe better to make them consistent?
2. no separate test example?

Thanks, it's just a draft, like I didn't do a lot of things yet, like docs/tests. It's just to explore a design idea. Whatever we decide in the end, I'll make everything polished.