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fix(core): support (message class, template) tuples in ChatPromptTemplate.from_messages #33989

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fix(core): support (message class, template) tuples in ChatPromptTemplate.from_messages #33989

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47d47c8
support (message class, template) tuples in ChatPromptTemplate.from_m…
hyattc1 Nov 16, 2025
8013ea6
fix(core): support message-class tuple conversion in ChatPromptTemplate
hyattc1 Nov 16, 2025
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8 changes: 8 additions & 0 deletions libs/core/langchain_core/prompts/chat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1433,6 +1433,14 @@ def _convert_to_message_template(
message_ = _create_template_from_message_type(
message_type_str, template, template_format=template_format
)
elif (
hasattr(message_type_str, "model_fields")
and "type" in message_type_str.model_fields
):
message_type = message_type_str.model_fields["type"].default
message_ = _create_template_from_message_type(
message_type, template, template_format=template_format
)
else:
message_ = message_type_str(
prompt=PromptTemplate.from_template(
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24 changes: 24 additions & 0 deletions libs/core/tests/unit_tests/prompts/test_chat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -317,6 +317,30 @@ def test_chat_prompt_template_from_messages_jinja2() -> None:
]


def test_chat_prompt_template_from_messages_using_message_classes() -> None:
"""Test creating a chat prompt template using message class tuples."""
template = ChatPromptTemplate.from_messages(
[
(SystemMessage, "You are a helpful AI bot. Your name is {name}."),
(HumanMessage, "Hello, how are you doing?"),
(AIMessage, "I'm doing well, thanks!"),
(HumanMessage, "{user_input}"),
]
)

expected = [
SystemMessage(
content="You are a helpful AI bot. Your name is Bob.", additional_kwargs={}
),
HumanMessage(content="Hello, how are you doing?", additional_kwargs={}),
AIMessage(content="I'm doing well, thanks!", additional_kwargs={}),
HumanMessage(content="What is your name?", additional_kwargs={}),
]

messages = template.format_messages(name="Bob", user_input="What is your name?")
assert messages == expected


@pytest.mark.requires("jinja2")
@pytest.mark.parametrize(
("template_format", "image_type_placeholder", "image_data_placeholder"),
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