Implement SquadQA tensorizer in TorchScript (#1211)

Summary:
Pull Request resolved: #1211

Implement SquadQA tensorizer in TorchScript

Differential Revision: D18801535

fbshipit-source-id: 1cc929424721eda444dcc20cda3e093b06d114e5

pytext/data/squad_for_bert_tensorizer.py

@@ -62,20 +62,8 @@ def _lookup_tokens(self, text: str, seq_len: int = None):
             max_seq_len=seq_len if seq_len else self.max_seq_len,
         )
 
-    def numberize(self, row):
-        question_column, doc_column = self.columns
-        doc_tokens, start_idx, end_idx = self._lookup_tokens(row[doc_column])
-        question_tokens, _, _ = self._lookup_tokens(row[question_column])
-        question_tokens = [self.vocab.get_bos_index()] + question_tokens
-        seq_lens = (len(question_tokens), len(doc_tokens))
-        segment_labels = ([i] * seq_len for i, seq_len in enumerate(seq_lens))
-        tokens = list(itertools.chain(question_tokens, doc_tokens))
-        segment_labels = list(itertools.chain(*segment_labels))
-        seq_len = len(tokens)
-        positions = list(range(seq_len))
-
+    def _calculate_answer_indices(self, row, offset, start_idx, end_idx):
         # now map original answer spans to tokenized spans
-        offset = len(question_tokens)
         start_idx_map = {}
         end_idx_map = {}
         for tokenized_idx, (raw_start_idx, raw_end_idx) in enumerate(
@@ -98,6 +86,25 @@ def numberize(self, row):
             answer_start_indices = [self.SPAN_PAD_IDX]
             answer_end_indices = [self.SPAN_PAD_IDX]
 
+        return answer_start_indices, answer_end_indices
+
+    def numberize(self, row):
+        question_column, doc_column = self.columns
+        doc_tokens, start_idx, end_idx = self._lookup_tokens(row[doc_column])
+        question_tokens, _, _ = self._lookup_tokens(row[question_column])
+        question_tokens = [self.vocab.get_bos_index()] + question_tokens
+        seq_lens = (len(question_tokens), len(doc_tokens))
+        segment_labels = ([i] * seq_len for i, seq_len in enumerate(seq_lens))
+        tokens = list(itertools.chain(question_tokens, doc_tokens))
+        segment_labels = list(itertools.chain(*segment_labels))
+        seq_len = len(tokens)
+        positions = list(range(seq_len))
+
+        # now map original answer spans to tokenized spans
+        offset = len(question_tokens)
+        answer_start_indices, answer_end_indices = self._calculate_answer_indices(
+            row, offset, start_idx, end_idx
+        )
         return (
             tokens,
             segment_labels,