Fix for #6431 - chatprompt template with partial variables giing validation error (#6456)

W.r.t recent changes, ChatPromptTemplate does not accepting partial
variables. This PR should fix that issue.


Fixes #6431




#### Who can review?



  @hwchase17

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

langchain/prompts/chat.py

@@ -168,6 +168,8 @@ class ChatPromptTemplate(BaseChatPromptTemplate, ABC):
         for message in messages:
             if isinstance(message, BaseMessagePromptTemplate):
                 input_vars.update(message.input_variables)
+        if "partial_variables" in values:
+            input_vars = input_vars - set(values["partial_variables"])
         if "input_variables" in values:
             if input_vars != set(values["input_variables"]):
                 raise ValueError(

tests/unit_tests/prompts/test_chat.py

@@ -162,3 +162,31 @@ def test_infer_variables() -> None:
     messages = [HumanMessagePromptTemplate.from_template("{foo}")]
     prompt = ChatPromptTemplate(messages=messages)
     assert prompt.input_variables == ["foo"]
+
+
+def test_chat_valid_with_partial_variables() -> None:
+    messages = [
+        HumanMessagePromptTemplate.from_template(
+            "Do something with {question} using {context} giving it like {formatins}"
+        )
+    ]
+    prompt = ChatPromptTemplate(
+        messages=messages,
+        input_variables=["question", "context"],
+        partial_variables={"formatins": "some structure"},
+    )
+    assert set(prompt.input_variables) == set(["question", "context"])
+    assert prompt.partial_variables == {"formatins": "some structure"}
+
+
+def test_chat_valid_infer_variables() -> None:
+    messages = [
+        HumanMessagePromptTemplate.from_template(
+            "Do something with {question} using {context} giving it like {formatins}"
+        )
+    ]
+    prompt = ChatPromptTemplate(
+        messages=messages, partial_variables={"formatins": "some structure"}
+    )
+    assert set(prompt.input_variables) == set(["question", "context"])
+    assert prompt.partial_variables == {"formatins": "some structure"}