Making TokenizerInterface more usable for the user's code.

Adding id_to_piece, piece_to_id and is_special_token functionality to TokenizerInterface and the corresponding implementations.

tokenizer.py

@@ -21,6 +21,15 @@ def bos_id(self):
     def eos_id(self):
         raise NotImplementedError("This method should be overridden by subclasses.")
 
+    def id_to_piece(self, token_id):
+        raise NotImplementedError("This method should be overridden by subclasses.")
+
+    def piece_to_id(self, token_str):
+        raise NotImplementedError("This method should be overridden by subclasses.")
+
+    def is_special_token(self, token_id):
+        raise NotImplementedError("This method should be overridden by subclasses.")
+
 class SentencePieceWrapper(TokenizerInterface):
     def __init__(self, model_path):
         super().__init__(model_path)
@@ -38,6 +47,17 @@ def bos_id(self):
     def eos_id(self):
         return self.processor.eos_id()
 
+    def id_to_piece(self, token_id):
+        return self.processor.id_to_piece(token_id).replace("▁", " ")
+
+    def piece_to_id(self, token_str):
+        return self.processor.piece_to_id(token_str.replace(" ", "▁"))
+
+    def is_special_token(self, token_id):
+        return self.processor.IsControl(token_id) \
+               or self.processor.IsUnknown(token_id) \
+               or self.processor.IsUnused(token_id)
+
 class TiktokenWrapper(TokenizerInterface):
     """
     Tokenizing and encoding/decoding text using the Tiktoken tokenizer.
@@ -53,7 +73,7 @@ def __init__(self, model_path):
         super().__init__(model_path)
         assert os.path.isfile(model_path), str(model_path)
         mergeable_ranks = load_tiktoken_bpe(str(model_path))
-        num_base_tokens = len(mergeable_ranks)
+        self.num_base_tokens = len(mergeable_ranks)
         special_tokens = [
             "<|begin_of_text|>",
             "<|end_of_text|>",
@@ -70,7 +90,7 @@ def __init__(self, model_path):
             for i in range(5, self.num_reserved_special_tokens - 5)
         ]
         self.special_tokens = {
-            token: num_base_tokens + i for i, token in enumerate(special_tokens)
+            token: self.num_base_tokens + i for i, token in enumerate(special_tokens)
         }
         self.model = tiktoken.Encoding(
             name=Path(model_path).name,
@@ -94,6 +114,15 @@ def bos_id(self):
     def eos_id(self):
         return self._eos_id
 
+    def id_to_piece(self, token_id):
+        return self.model.decode([token_id])
+
+    def piece_to_id(self, token_str):
+        return self.model.encode_single_token(token_str)
+
+    def is_special_token(self, token_id):
+        return token_id >= self.num_base_tokens and token_id < self.num_base_tokens + len(self.special_tokens)
+
 def get_tokenizer(tokenizer_model_path, model_name):
     """
     Factory function to get the appropriate tokenizer based on the model name.