Unable to find the word that I added to the Huggingface Bert tokenizer vocabulary

Question

I tried to add new words to the Bert tokenizer vocab. I see that the length of the vocab is increasing, however I can't find the newly added word in the vocab.

tokenizer.add_tokens(['covid', 'wuhan'])

v = tokenizer.get_vocab()

print(len(v))
'covid' in tokenizer.vocab

Output:

30524

False

Answer 1

You are calling two different things with tokenizer.vocab and tokenizer.get_vocab(). The first one contains the base vocabulary without the added tokens, while the other one contains the base vocabulary with the added tokens.

from transformers import BertTokenizer

t = BertTokenizer.from_pretrained('bert-base-uncased')

print(len(t.vocab))
print(len(t.get_vocab()))
print(t.get_added_vocab())
t.add_tokens(['covid'])
print(len(t.vocab))
print(len(t.get_vocab()))
print(t.get_added_vocab())

Output:

30522
30522
{}
30522
30523
{'covid': 30522}