Add from_file class method to the Prompt object

Fix #1345

outlines/__init__.py

@@ -1,4 +1,5 @@
 """Outlines is a Generative Model Programming Framework."""
+
 import outlines.generate
 import outlines.grammars
 import outlines.models
@@ -7,14 +8,15 @@
 from outlines.base import vectorize
 from outlines.caching import clear_cache, disable_cache, get_cache
 from outlines.function import Function
-from outlines.prompts import prompt
+from outlines.prompts import Prompt, prompt
 
 __all__ = [
     "clear_cache",
     "disable_cache",
     "get_cache",
     "Function",
     "prompt",
+    "Prompt",
     "vectorize",
     "grammars",
 ]

outlines/prompts.py

@@ -1,12 +1,13 @@
 import functools
 import inspect
 import json
+import os
 import re
 import textwrap
 from dataclasses import dataclass
 from typing import Any, Callable, Dict, List, Optional, Type, cast
 
-from jinja2 import Environment, StrictUndefined
+from jinja2 import Environment, FileSystemLoader, StrictUndefined, meta
 from pydantic import BaseModel
 
 
@@ -41,6 +42,33 @@ def __call__(self, *args, **kwargs) -> str:
     def __str__(self):
         return self.template
 
+    @classmethod
+    def from_file(cls, filename: str):
+        """Create a Prompt instance from a file containing a Jinja template."""
+        with open(filename) as file:
+            template = file.read()
+
+        # Determine the directory of the file
+        file_directory = os.path.dirname(os.path.abspath(filename))
+
+        # Create a Jinja environment to parse the template
+        env = Environment(
+            loader=FileSystemLoader(file_directory),
+            trim_blocks=True,
+            lstrip_blocks=True,
+        )
+        parsed_content = env.parse(template)
+        variables = meta.find_undeclared_variables(parsed_content)
+
+        # Create a signature with the variables as parameters
+        parameters = [
+            inspect.Parameter(var, inspect.Parameter.POSITIONAL_OR_KEYWORD)
+            for var in variables
+        ]
+        signature = inspect.Signature(parameters)
+
+        return cls(template, signature)
+
 
 def prompt(fn: Callable) -> Prompt:
     """Decorate a function that contains a prompt template.

tests/test_prompts.py

@@ -1,10 +1,12 @@
+import os
+import tempfile
 from typing import Dict, List
 
 import pytest
 from pydantic import BaseModel, Field
 
 import outlines
-from outlines.prompts import render
+from outlines.prompts import Prompt, render
 
 
 def test_render():
@@ -312,3 +314,59 @@ def args_prompt(fn):
         args_prompt(with_all)
         == "args: x1, y1, z1, x2: bool, y2: str, z2: Dict[int, List[str]], x3=True, y3='Hi', z3={4: ['I', 'love', 'outlines']}, x4: bool = True, y4: str = 'Hi', z4: Dict[int, List[str]] = {4: ['I', 'love', 'outlines']}"
     )
+
+
+@pytest.fixture
+def temp_prompt_file():
+    # Create a temporary directory
+    with tempfile.TemporaryDirectory() as test_dir:
+        # Create a temporary prompt file
+        prompt_file_path = os.path.join(test_dir, "prompt.txt")
+        with open(prompt_file_path, "w") as f:
+            f.write(
+                """Here is a prompt with examples:
+
+{% for example in examples %}
+- Q: {{ example.question }}
+- A: {{ example.answer }}
+{% endfor %}
+
+Now please answer the following question:
+
+Q: {{ question }}
+A:
+"""
+            )
+        yield prompt_file_path
+
+
+def test_prompt_from_file(temp_prompt_file):
+    # Create a Prompt instance from the file
+    template = Prompt.from_file(temp_prompt_file)
+
+    # Define example data
+    examples = [
+        {"question": "What is the capital of France?", "answer": "Paris"},
+        {"question": "What is 2 + 2?", "answer": "4"},
+    ]
+    question = "What is the Earth's diameter?"
+
+    # Render the template
+    rendered_prompt = template(examples=examples, question=question)
+
+    # Expected output
+    expected_output = """Here is a prompt with examples:
+
+- Q: What is the capital of France?
+- A: Paris
+- Q: What is 2 + 2?
+- A: 4
+
+Now please answer the following question:
+
+Q: What is the Earth's diameter?
+A:
+"""
+
+    # Assert the rendered prompt matches the expected output
+    assert rendered_prompt.strip() == expected_output.strip()