From f2f2aced6daf0eb73f2c0bf4a9d1d4b5322de4a7 Mon Sep 17 00:00:00 2001
From: Harrison Chase <hw.chase.17@gmail.com>
Date: Sat, 13 May 2023 21:47:20 -0700
Subject: [PATCH] allow partials in from_template (#4638)

---
 langchain/prompts/prompt.py           |  6 ++++++
 tests/unit_tests/prompts/test_chat.py | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/langchain/prompts/prompt.py b/langchain/prompts/prompt.py
index c61cf69f81..31f87d43b9 100644
--- a/langchain/prompts/prompt.py
+++ b/langchain/prompts/prompt.py
@@ -135,6 +135,12 @@ class PromptTemplate(StringPromptTemplate):
                 v for _, v, _, _ in Formatter().parse(template) if v is not None
             }
 
+        if "partial_variables" in kwargs:
+            partial_variables = kwargs["partial_variables"]
+            input_variables = {
+                var for var in input_variables if var not in partial_variables
+            }
+
         return cls(
             input_variables=list(sorted(input_variables)), template=template, **kwargs
         )
diff --git a/tests/unit_tests/prompts/test_chat.py b/tests/unit_tests/prompts/test_chat.py
index 6defde6991..87f64c9599 100644
--- a/tests/unit_tests/prompts/test_chat.py
+++ b/tests/unit_tests/prompts/test_chat.py
@@ -56,6 +56,30 @@ def create_chat_prompt_template() -> ChatPromptTemplate:
     )
 
 
+def test_create_chat_prompt_template_from_template() -> None:
+    """Create a chat prompt template."""
+    prompt = ChatPromptTemplate.from_template("hi {foo} {bar}")
+    assert prompt.messages == [
+        HumanMessagePromptTemplate.from_template("hi {foo} {bar}")
+    ]
+
+
+def test_create_chat_prompt_template_from_template_partial() -> None:
+    """Create a chat prompt template with partials."""
+    prompt = ChatPromptTemplate.from_template(
+        "hi {foo} {bar}", partial_variables={"foo": "jim"}
+    )
+    expected_prompt = PromptTemplate(
+        template="hi {foo} {bar}",
+        input_variables=["bar"],
+        partial_variables={"foo": "jim"},
+    )
+    assert len(prompt.messages) == 1
+    output_prompt = prompt.messages[0]
+    assert isinstance(output_prompt, HumanMessagePromptTemplate)
+    assert output_prompt.prompt == expected_prompt
+
+
 def test_chat_prompt_template() -> None:
     """Test chat prompt template."""
     prompt_template = create_chat_prompt_template()