Development: Add truncate function

app/services/guidance_functions.py

@@ -0,0 +1,8 @@
+def truncate(history: list[any], max_length: int):
+    if max_length == 0:
+        return []
+
+    if max_length > 0:
+        return history[:max_length]
+
+    return history[max_length:]

app/services/guidance_wrapper.py

@@ -2,6 +2,7 @@
 
 from app.config import LLMModelConfig
 from app.models.dtos import Content, ContentType
+from app.services.guidance_functions import truncate
 
 
 class GuidanceWrapper:
@@ -34,6 +35,7 @@ def query(self) -> Content:
         template = guidance(self.handlebars)
         result = template(
             llm=self._get_llm(),
+            truncate=truncate,
             **self.parameters,
         )
 

tests/services/guidance_functions_test.py

@@ -0,0 +1,21 @@
+import pytest
+from app.services.guidance_functions import truncate
+
+
+@pytest.mark.parametrize(
+    "history,max_length,expected",
+    [
+        ([], -2, []),
+        ([], 0, []),
+        ([], 2, []),
+        ([1, 2, 3], 0, []),
+        # Get the last n elements
+        ([1, 2, 3], -4, [1, 2, 3]),
+        ([1, 2, 3], -2, [2, 3]),
+        # Get the first n elements
+        ([1, 2, 3], 2, [1, 2]),
+        ([1, 2, 3], 4, [1, 2, 3]),
+    ],
+)
+def test_truncate(history, max_length, expected):
+    assert truncate(history, max_length) == expected

tests/services/guidance_wrapper_test.py

@@ -34,6 +34,32 @@ def test_query_success(mocker):
     assert result.text_content == "the output"
 
 
+def test_query_using_truncate_function(mocker):
+    mocker.patch.object(
+        GuidanceWrapper,
+        "_get_llm",
+        return_value=guidance.llms.Mock("the output"),
+    )
+
+    handlebars = """{{#user~}}I want a response to the following query:
+    {{query}}{{~/user}}{{#assistant~}}
+    {{gen 'answer' temperature=0.0 max_tokens=500}}{{~/assistant}}
+    {{set 'response' (truncate answer 3)}}
+    """
+
+    guidance_wrapper = GuidanceWrapper(
+        model=llm_model_config,
+        handlebars=handlebars,
+        parameters={"query": "Some query"},
+    )
+
+    result = guidance_wrapper.query()
+
+    assert isinstance(result, Content)
+    assert result.type == ContentType.TEXT
+    assert result.text_content == "the"
+
+
 def test_query_missing_required_params(mocker):
     mocker.patch.object(
         GuidanceWrapper,