From 8a5ec894e7cbca6a47afd195cce2a0e3c75e052b Mon Sep 17 00:00:00 2001
From: Edmar Ferreira <edmaroferreira@gmail.com>
Date: Sun, 13 Nov 2022 18:15:30 -0300
Subject: [PATCH] Prompt from file proof of concept using plain text (#127)

This is a simple proof of concept of using external files as templates.
I'm still feeling my way around the codebase.
As a user, I want to use files as prompts, so it will be easier to
manage and test prompts.
The future direction is to use a template engine, most likely Mako.
---
 langchain/prompts/prompt.py           | 15 +++++++++++++++
 tests/unit_tests/data/prompt_file.txt |  2 ++
 tests/unit_tests/test_prompt.py       |  8 ++++++++
 3 files changed, 25 insertions(+)
 create mode 100644 tests/unit_tests/data/prompt_file.txt

diff --git a/langchain/prompts/prompt.py b/langchain/prompts/prompt.py
index 02f87b77003..b84b7718149 100644
--- a/langchain/prompts/prompt.py
+++ b/langchain/prompts/prompt.py
@@ -97,3 +97,18 @@ class Prompt(BaseModel, BasePrompt):
         example_str = example_separator.join(examples)
         template = prefix + example_str + suffix
         return cls(input_variables=input_variables, template=template)
+
+    @classmethod
+    def from_file(cls, template_file: str, input_variables: List[str]) -> "Prompt":
+        """Load a prompt from a file.
+
+        Args:
+            template_file: The path to the file containing the prompt template.
+            input_variables: A list of variable names the final prompt template
+                will expect.
+        Returns:
+            The prompt loaded from the file.
+        """
+        with open(template_file, "r") as f:
+            template = f.read()
+        return cls(input_variables=input_variables, template=template)
diff --git a/tests/unit_tests/data/prompt_file.txt b/tests/unit_tests/data/prompt_file.txt
new file mode 100644
index 00000000000..0681c36f48e
--- /dev/null
+++ b/tests/unit_tests/data/prompt_file.txt
@@ -0,0 +1,2 @@
+Question: {question}
+Answer:
\ No newline at end of file
diff --git a/tests/unit_tests/test_prompt.py b/tests/unit_tests/test_prompt.py
index 45040793626..80a7fca4a75 100644
--- a/tests/unit_tests/test_prompt.py
+++ b/tests/unit_tests/test_prompt.py
@@ -77,3 +77,11 @@ def test_prompt_invalid_template_format() -> None:
         Prompt(
             input_variables=input_variables, template=template, template_format="bar"
         )
+
+
+def test_prompt_from_file() -> None:
+    """Test prompt can be successfully constructed from a file."""
+    template_file = "tests/unit_tests/data/prompt_file.txt"
+    input_variables = ["question"]
+    prompt = Prompt.from_file(template_file, input_variables)
+    assert prompt.template == "Question: {question}\nAnswer:"