Upload tokenizer.py

tokenizer.py

@@ -0,0 +1,108 @@
+import torch
+from abc import ABC, abstractmethod
+from typing import List, Optional, Tuple
+from torch import Tensor
+from torch.nn.utils.rnn import pad_sequence
+
+
+class BaseTokenizer(ABC):
+
+    def __init__(self, charset: str, specials_first: tuple = (), specials_last: tuple = ()) -> None:
+        self._itos = specials_first + tuple(charset + '[UNK]') + specials_last
+        self._stoi = {s: i for i, s in enumerate(self._itos)}
+
+    def __len__(self):
+        return len(self._itos)
+
+    def _tok2ids(self, tokens: str) -> List[int]:
+        return [self._stoi[s] for s in tokens]
+
+    def _ids2tok(self, token_ids: List[int], join: bool = True) -> str:
+        tokens = [self._itos[i] for i in token_ids]
+        return ''.join(tokens) if join else tokens
+
+    @abstractmethod
+    def encode(self, labels: List[str], device: Optional[torch.device] = None) -> Tensor:
+        raise NotImplementedError
+
+    @abstractmethod
+    def _filter(self, probs: Tensor, ids: Tensor) -> Tuple[Tensor, List[int]]:
+        """Internal method which performs the necessary filtering prior to decoding."""
+        raise NotImplementedError
+
+    def decode(self, token_dists: Tensor, beam_width: int = 1, raw: bool = False) -> Tuple[List[str], List[Tensor]]:
+        if beam_width > 1:
+            return self.beam_search_decode(token_dists, beam_width, raw)
+        else:
+            return self.greedy_decode(token_dists, raw)
+
+    def greedy_decode(self, token_dists: Tensor, raw: bool = False) -> Tuple[List[str], List[Tensor]]:
+        batch_tokens = []
+        batch_probs = []
+        for dist in token_dists:
+            probs, ids = dist.max(-1)  # greedy selection
+            if not raw:
+                probs, ids = self._filter(probs, ids)
+            tokens = self._ids2tok(ids, not raw)
+            batch_tokens.append(tokens)
+            batch_probs.append(probs)
+        return batch_tokens, batch_probs
+
+    def beam_search_decode(self, token_dists: Tensor, beam_width: int, raw: bool) -> Tuple[List[str], List[Tensor]]:
+     batch_tokens = []
+     batch_probs = []
+
+     for dist in token_dists:
+        sequences = [([], 1.0)]
+        for step_dist in dist:
+            all_candidates = []
+            for seq, score in sequences:
+                top_probs, top_ids = step_dist.topk(beam_width)
+                for i in range(beam_width):
+                    candidate = (seq + [top_ids[i].item()],
+                                 score * top_probs[i].item())
+                    all_candidates.append(candidate)
+            ordered = sorted(all_candidates, key=lambda x: x[1], reverse=True)
+            sequences = ordered[:beam_width]
+
+        best_sequence, best_score = sequences[0]
+        if not raw:
+            best_score_tensor = torch.tensor([best_score])
+            best_sequence_tensor = torch.tensor(best_sequence)
+            best_score_tensor, best_sequence = self._filter(
+                best_score_tensor, best_sequence_tensor)
+            best_score = best_score_tensor.item()
+        tokens = self._ids2tok(best_sequence, not raw)
+        batch_tokens.append(tokens)
+        batch_probs.append(best_score)
+
+     return batch_tokens, batch_probs
+
+
+class Tokenizer(BaseTokenizer):
+    BOS = '[B]'
+    EOS = '[E]'
+    PAD = '[P]'
+
+    def __init__(self, charset: str) -> None:
+        specials_first = (self.EOS,)
+        specials_last = (self.BOS, self.PAD)
+        super().__init__(charset, specials_first, specials_last)
+        self.eos_id, self.bos_id, self.pad_id = [
+            self._stoi[s] for s in specials_first + specials_last]
+
+    def encode(self, labels: List[str], device: Optional[torch.device] = None) -> Tensor:
+        batch = [torch.as_tensor([self.bos_id] + self._tok2ids(y) + [self.eos_id], dtype=torch.long, device=device)
+                 for y in labels]
+        return pad_sequence(batch, batch_first=True, padding_value=self.pad_id)
+
+    def _filter(self, probs: Tensor, ids: Tensor) -> Tuple[Tensor, List[int]]:
+        ids = ids.tolist()
+        try:
+            eos_idx = ids.index(self.eos_id)
+        except ValueError:
+            eos_idx = len(ids)
+        # Truncate after EOS
+        ids = ids[:eos_idx]
+        probs = probs[:eos_idx + 1]  # but include prob. for EOS (if it exists)
+        return probs, ids