Function●Since v0.1

get_buffer_string

get_buffer_string(
  messages: Sequence[BaseMessage],
  human_prefix: str = 'Human',
  ai_prefix:

View source on GitHub

Parameters

Name	Type	Description
`messages`*	`Sequence[BaseMessage]`	Messages to be converted to strings.
`human_prefix`	`str`	Default:`'Human'` The prefix to prepend to contents of `HumanMessage`s.
`ai_prefix`	`str`	Default:`'AI'`
`system_prefix`	`str`	Default:`'System'`
`function_prefix`	`str`	Default:`'Function'`
`tool_prefix`	`str`	Default:`'Tool'`
`message_separator`	`str`	Default:`'\n'`
`format`	`Literal['prefix', 'xml']`	Default:`'prefix'`

Warning

If a message is an AIMessage and contains both tool calls under tool_calls and a function call under additional_kwargs["function_call"], only the tool calls will be appended to the string representation.

XML format

When using format='xml':

All messages use uniform <message type="role">content</message> format.
The type attribute uses human_prefix (lowercased) for HumanMessage, ai_prefix (lowercased) for AIMessage, system_prefix (lowercased) for SystemMessage, function_prefix (lowercased) for FunctionMessage, tool_prefix (lowercased) for ToolMessage, and the original role (unchanged) for ChatMessage.
Message content is escaped using xml.sax.saxutils.escape().
Attribute values are escaped using xml.sax.saxutils.quoteattr().
AI messages with tool calls use nested structure with <content> and <tool_call> elements.
For multi-modal content (list of content blocks), supported block types are: text, reasoning, image (URL/file_id only), image_url (OpenAI-style, URL only), audio (URL/file_id only), video (URL/file_id only), text-plain, server_tool_call, and server_tool_result.
Content blocks with base64-encoded data are skipped (including blocks with base64 field or data: URLs).
Unknown block types are skipped.
Plain text document content (text-plain), server tool call arguments, and server tool result outputs are truncated to 500 characters.

Example:

Default prefix format:

from langchain_core.messages import AIMessage, HumanMessage, get_buffer_string

messages = [
    HumanMessage(content="Hi, how are you?"),
    AIMessage(content="Good, how are you?"),
]
get_buffer_string(messages)
# -> "Human: Hi, how are you?\nAI: Good, how are you?"

XML format (useful when content contains role-like prefixes):

messages = [
    HumanMessage(content="Example: Human: some text"),
    AIMessage(content="I see the example."),
]
get_buffer_string(messages, format="xml")
# -> '<message type="human">Example: Human: some text</message>\\n'
# -> '<message type="ai">I see the example.</message>'

XML format with special characters (automatically escaped):

messages = [
    HumanMessage(content="Is 5 < 10 & 10 > 5?"),
]
get_buffer_string(messages, format="xml")
# -> '<message type="human">Is 5 &lt; 10 &amp; 10 &gt; 5?</message>'

XML format with tool calls:

messages = [
    AIMessage(
        content="I'll search for that.",
        tool_calls=[
            {"id": "call_123", "name": "search", "args": {"query": "weather"}}
        ],
    ),
]
get_buffer_string(messages, format="xml")
# -> '<message type="ai">\\n'
# -> '  <content>I\\'ll search for that.</content>\\n'
# -> '  <tool_call id="call_123" name="search">'
# -> '{"query": "weather"}</tool_call>\\n'
# -> '</message>'

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get_buffer_string

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