def indices_to_tokens(self, indexed_tokens: IndexedTokenList,
vocabulary: Vocabulary) -> List[Token]:
token_ids = indexed_tokens["token_ids"]
type_ids = indexed_tokens.get("type_ids")
return [
Token(
text=vocabulary.get_token_from_index(token_ids[i],
self._namespace),
text_id=token_ids[i],
type_id=type_ids[i] if type_ids is not None else None,
) for i in range(len(token_ids))
]
def _postprocess_output(self, output: IndexedTokenList) -> IndexedTokenList:
"""
Takes an IndexedTokenList about to be returned by `tokens_to_indices()` and adds any
necessary postprocessing, e.g. long sequence splitting.
The input should have a `"token_ids"` key corresponding to the token indices. They should
have special tokens already inserted.
"""
if self._max_length is not None:
# We prepare long indices by converting them to (assuming max_length == 5)
# [CLS] A B C [SEP] [CLS] D E F [SEP] ...
# Embedder is responsible for folding this 1-d sequence to 2-d and feed to the
# transformer model.
# TODO(zhaofengw): we aren't respecting word boundaries when segmenting wordpieces.
indices = output["token_ids"]
type_ids = output.get("type_ids", [0] * len(indices))
# Strips original special tokens
indices = indices[
self._num_added_start_tokens : len(indices) - self._num_added_end_tokens
]
type_ids = type_ids[
self._num_added_start_tokens : len(type_ids) - self._num_added_end_tokens
]
# Folds indices
folded_indices = [
indices[i : i + self._effective_max_length]
for i in range(0, len(indices), self._effective_max_length)
]
folded_type_ids = [
type_ids[i : i + self._effective_max_length]
for i in range(0, len(type_ids), self._effective_max_length)
]
# Adds special tokens to each segment
folded_indices = [
self._tokenizer.build_inputs_with_special_tokens(segment)
for segment in folded_indices
]
single_sequence_start_type_ids = [
t.type_id for t in self._allennlp_tokenizer.single_sequence_start_tokens
]
single_sequence_end_type_ids = [
t.type_id for t in self._allennlp_tokenizer.single_sequence_end_tokens
]
folded_type_ids = [
single_sequence_start_type_ids + segment + single_sequence_end_type_ids
for segment in folded_type_ids
]
assert all(
len(segment_indices) == len(segment_type_ids)
for segment_indices, segment_type_ids in zip(folded_indices, folded_type_ids)
)
# Flattens
indices = [i for segment in folded_indices for i in segment]
type_ids = [i for segment in folded_type_ids for i in segment]
output["token_ids"] = indices
output["type_ids"] = type_ids
output["segment_concat_mask"] = [True] * len(indices)
return output
