ChatPromptTemplate Class — langchain Architecture

Source Code

libs/core/langchain_core/prompts/chat.py lines 789–1327

class ChatPromptTemplate(BaseChatPromptTemplate):
    """Prompt template for chat models.

    Use to create flexible templated prompts for chat models.

    !!! example

        ```python
        from langchain_core.prompts import ChatPromptTemplate

        template = ChatPromptTemplate(
            [
                ("system", "You are a helpful AI bot. Your name is {name}."),
                ("human", "Hello, how are you doing?"),
                ("ai", "I'm doing well, thanks!"),
                ("human", "{user_input}"),
            ]
        )

        prompt_value = template.invoke(
            {
                "name": "Bob",
                "user_input": "What is your name?",
            }
        )
        # Output:
        # ChatPromptValue(
        #    messages=[
        #        SystemMessage(content='You are a helpful AI bot. Your name is Bob.'),
        #        HumanMessage(content='Hello, how are you doing?'),
        #        AIMessage(content="I'm doing well, thanks!"),
        #        HumanMessage(content='What is your name?')
        #    ]
        # )
        ```

    !!! note "Messages Placeholder"

        ```python
        # In addition to Human/AI/Tool/Function messages,
        # you can initialize the template with a MessagesPlaceholder
        # either using the class directly or with the shorthand tuple syntax:

        template = ChatPromptTemplate(
            [
                ("system", "You are a helpful AI bot."),
                # Means the template will receive an optional list of messages under
                # the "conversation" key
                ("placeholder", "{conversation}"),
                # Equivalently:
                # MessagesPlaceholder(variable_name="conversation", optional=True)
            ]
        )

        prompt_value = template.invoke(
            {
                "conversation": [
                    ("human", "Hi!"),
                    ("ai", "How can I assist you today?"),
                    ("human", "Can you make me an ice cream sundae?"),
                    ("ai", "No."),
                ]
            }
        )

        # Output:
        # ChatPromptValue(
        #    messages=[
        #        SystemMessage(content='You are a helpful AI bot.'),
        #        HumanMessage(content='Hi!'),
        #        AIMessage(content='How can I assist you today?'),
        #        HumanMessage(content='Can you make me an ice cream sundae?'),
        #        AIMessage(content='No.'),
        #    ]
        # )
        ```

    !!! note "Single-variable template"

        If your prompt has only a single input variable (i.e., one instance of
        `'{variable_nams}'`), and you invoke the template with a non-dict object, the