refactor: avoid downloading tokenizer if truncate is False (#1152)

* avoid downloading tokenizer if truncate is False

* fix

integrations/amazon_bedrock/src/haystack_integrations/components/generators/amazon_bedrock/generator.py

@@ -152,15 +152,16 @@ def resolve_secret(secret: Optional[Secret]) -> Optional[str]:
         # We pop the model_max_length as it is not sent to the model but used to truncate the prompt if needed
         model_max_length = kwargs.get("model_max_length", 4096)
 
-        # Truncate prompt if prompt tokens > model_max_length-max_length
-        # (max_length is the length of the generated text)
-        # we use GPT2 tokenizer which will likely provide good token count approximation
-
-        self.prompt_handler = DefaultPromptHandler(
-            tokenizer="gpt2",
-            model_max_length=model_max_length,
-            max_length=self.max_length or 100,
-        )
+        # we initialize the prompt handler only if truncate is True: we avoid unnecessarily downloading the tokenizer
+        if self.truncate:
+            # Truncate prompt if prompt tokens > model_max_length-max_length
+            # (max_length is the length of the generated text)
+            # we use GPT2 tokenizer which will likely provide good token count approximation
+            self.prompt_handler = DefaultPromptHandler(
+                tokenizer="gpt2",
+                model_max_length=model_max_length,
+                max_length=self.max_length or 100,
+            )
 
         model_adapter_cls = self.get_model_adapter(model=model)
         if not model_adapter_cls:

integrations/amazon_bedrock/tests/test_generator.py

@@ -108,6 +108,14 @@ def test_constructor_prompt_handler_initialized(mock_boto3_session, mock_prompt_
     assert layer.prompt_handler.model_max_length == 4096
 
 
+def test_prompt_handler_absent_when_truncate_false(mock_boto3_session):
+    """
+    Test that the prompt_handler is not initialized when truncate is set to False.
+    """
+    generator = AmazonBedrockGenerator(model="anthropic.claude-v2", truncate=False)
+    assert not hasattr(generator, "prompt_handler")
+
+
 def test_constructor_with_model_kwargs(mock_boto3_session):
     """
     Test that model_kwargs are correctly set in the constructor