How to share vocabulary across fields?

I’m new to torchtext. I want to use two fields which should have the same vocabulary. The only difference is that field2 prepends an <sos> token to every sequence. I have the following code:

field1 = ReversibleField(torch.LongTensor, tokenize=tokenizer)
field2 = ReversibleField(torch.LongTensor, tokenize=tokenizer, init_token='<sos>')
dataset = TabularDataset(path='train.json', format='json',
                         fields={'x': ('x', field1),  'y': ('y', field2)})
field1.build_vocab(dataset, max_size=30000)

Now I want field2 to use the vocab of field1. I tried field2.vocab = field1.vocab, but this results in an error in later processing. According to documentation, the only way to force the same vocabulary seems to be to use the same field, but setting the init_token dynamically isn’t possible when the dataset is read by a BucketIterator.

My current workaround is to first save field1, and then load it also as field2:

field1 = ReversibleField(torch.LongTensor, tokenize=tokenizer, init_token='<sos>')
# ... build vocab as before
torch.save(field1, 'field1.pt')
field2 = torch.load('field1.pt')
field1.init_token = None

However, I don’t know if this will also work if the fields are associated with word vectors. Since the vocab of field1 and field2 are essentially two independent copies, updates to the word embeddings will have to be performed on both fields. Alternatively, I can manually create a vocabulary dict and use it to initialize two copies of Vocab, but how can I make the two fields to use them?

Is there a recommended way to share vocabulary?

[hohoCode]

Exactly the same question, is there any official way to share vocabulary ACROSS fields? Thanks!

[yyHaker]

I think this maybe is a method!