langchain_core.prompts.chat.MessagesPlaceholder¶

class langchain_core.prompts.chat.MessagesPlaceholder[source]¶

Bases: BaseMessagePromptTemplate

Prompt template that assumes variable is already list of messages.

A placeholder which can be used to pass in a list of messages.

Direct usage:

from langchain_core.prompts import MessagesPlaceholder

prompt = MessagesPlaceholder("history")
prompt.format_messages() # raises KeyError

prompt = MessagesPlaceholder("history", optional=True)
prompt.format_messages() # returns empty list []

prompt.format_messages(
    history=[
        ("system", "You are an AI assistant."),
        ("human", "Hello!"),
    ]
)
# -> [
#     SystemMessage(content="You are an AI assistant."),
#     HumanMessage(content="Hello!"),
# ]

Building a prompt with chat history:

from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder

prompt = ChatPromptTemplate.from_messages(
    [
        ("system", "You are a helpful assistant."),
        MessagesPlaceholder("history"),
        ("human", "{question}")
    ]
)
prompt.invoke(
   {
       "history": [("human", "what's 5 + 2"), ("ai", "5 + 2 is 7")],
       "question": "now multiply that by 4"
   }
)
# -> ChatPromptValue(messages=[
#     SystemMessage(content="You are a helpful assistant."),
#     HumanMessage(content="what's 5 + 2"),
#     AIMessage(content="5 + 2 is 7"),
#     HumanMessage(content="now multiply that by 4"),
# ])

Create a new model by parsing and validating input data from keyword arguments.

Raises ValidationError if the input data cannot be parsed to form a valid model.

param optional: bool = False¶

If True format_messages can be called with no arguments and will return an empty list. If False then a named argument with name variable_name must be passed in, even if the value is an empty list.

param variable_name: str [Required]¶

Name of variable to use as messages.

async aformat_messages(**kwargs: Any) List[BaseMessage]¶

Format messages from kwargs. Should return a list of BaseMessages.

Parameters

**kwargs (Any) – Keyword arguments to use for formatting.

Returns

List of BaseMessages.

Return type

List[BaseMessage]

classmethod construct(_fields_set: Optional[SetStr] = None, **values: Any) Model¶

Creates a new model setting __dict__ and __fields_set__ from trusted or pre-validated data. Default values are respected, but no other validation is performed. Behaves as if Config.extra = ‘allow’ was set since it adds all passed values

Parameters
  • _fields_set (Optional[SetStr]) –

  • values (Any) –

Return type

Model

copy(*, include: Optional[Union[AbstractSetIntStr, MappingIntStrAny]] = None, exclude: Optional[Union[AbstractSetIntStr, MappingIntStrAny]] = None, update: Optional[DictStrAny] = None, deep: bool = False) Model¶

Duplicate a model, optionally choose which fields to include, exclude and change.

Parameters
  • include (Optional[Union[AbstractSetIntStr, MappingIntStrAny]]) – fields to include in new model

  • exclude (Optional[Union[AbstractSetIntStr, MappingIntStrAny]]) – fields to exclude from new model, as with values this takes precedence over include

  • update (Optional[DictStrAny]) – values to change/add in the new model. Note: the data is not validated before creating the new model: you should trust this data

  • deep (bool) – set to True to make a deep copy of the model

  • self (Model) –

Returns

new model instance

Return type

Model

dict(*, include: Optional[Union[AbstractSetIntStr, MappingIntStrAny]] = None, exclude: Optional[Union[AbstractSetIntStr, MappingIntStrAny]] = None, by_alias: bool = False, skip_defaults: Optional[bool] = None, exclude_unset: bool = False, exclude_defaults: bool = False, exclude_none: bool = False) DictStrAny¶

Generate a dictionary representation of the model, optionally specifying which fields to include or exclude.

Parameters
  • include (Optional[Union[AbstractSetIntStr, MappingIntStrAny]]) –

  • exclude (Optional[Union[AbstractSetIntStr, MappingIntStrAny]]) –

  • by_alias (bool) –

  • skip_defaults (Optional[bool]) –

  • exclude_unset (bool) –

  • exclude_defaults (bool) –

  • exclude_none (bool) –

Return type

DictStrAny

format_messages(**kwargs: Any) List[BaseMessage][source]¶

Format messages from kwargs.

Parameters

**kwargs (Any) – Keyword arguments to use for formatting.

Returns

List of BaseMessage.

Return type

List[BaseMessage]

classmethod from_orm(obj: Any) Model¶
Parameters

obj (Any) –

Return type

Model

classmethod get_lc_namespace() List[str][source]¶

Get the namespace of the langchain object.

Return type

List[str]

classmethod is_lc_serializable() bool¶

Return whether or not the class is serializable.

Return type

bool

json(*, include: Optional[Union[AbstractSetIntStr, MappingIntStrAny]] = None, exclude: Optional[Union[AbstractSetIntStr, MappingIntStrAny]] = None, by_alias: bool = False, skip_defaults: Optional[bool] = None, exclude_unset: bool = False, exclude_defaults: bool = False, exclude_none: bool = False, encoder: Optional[Callable[[Any], Any]] = None, models_as_dict: bool = True, **dumps_kwargs: Any) unicode¶

Generate a JSON representation of the model, include and exclude arguments as per dict().

encoder is an optional function to supply as default to json.dumps(), other arguments as per json.dumps().

Parameters
  • include (Optional[Union[AbstractSetIntStr, MappingIntStrAny]]) –

  • exclude (Optional[Union[AbstractSetIntStr, MappingIntStrAny]]) –

  • by_alias (bool) –

  • skip_defaults (Optional[bool]) –

  • exclude_unset (bool) –

  • exclude_defaults (bool) –

  • exclude_none (bool) –

  • encoder (Optional[Callable[[Any], Any]]) –

  • models_as_dict (bool) –

  • dumps_kwargs (Any) –

Return type

unicode

classmethod lc_id() List[str]¶

A unique identifier for this class for serialization purposes.

The unique identifier is a list of strings that describes the path to the object.

Return type

List[str]

classmethod parse_file(path: Union[str, Path], *, content_type: unicode = None, encoding: unicode = 'utf8', proto: Protocol = None, allow_pickle: bool = False) Model¶
Parameters
  • path (Union[str, Path]) –

  • content_type (unicode) –

  • encoding (unicode) –

  • proto (Protocol) –

  • allow_pickle (bool) –

Return type

Model

classmethod parse_obj(obj: Any) Model¶
Parameters

obj (Any) –

Return type

Model

classmethod parse_raw(b: Union[str, bytes], *, content_type: unicode = None, encoding: unicode = 'utf8', proto: Protocol = None, allow_pickle: bool = False) Model¶
Parameters
  • b (Union[str, bytes]) –

  • content_type (unicode) –

  • encoding (unicode) –

  • proto (Protocol) –

  • allow_pickle (bool) –

Return type

Model

pretty_print() None¶
Return type

None

pretty_repr(html: bool = False) str[source]¶

Human-readable representation.

Parameters

html (bool) –

Return type

str

classmethod schema(by_alias: bool = True, ref_template: unicode = '#/definitions/{model}') DictStrAny¶
Parameters
  • by_alias (bool) –

  • ref_template (unicode) –

Return type

DictStrAny

classmethod schema_json(*, by_alias: bool = True, ref_template: unicode = '#/definitions/{model}', **dumps_kwargs: Any) unicode¶
Parameters
  • by_alias (bool) –

  • ref_template (unicode) –

  • dumps_kwargs (Any) –

Return type

unicode

to_json() Union[SerializedConstructor, SerializedNotImplemented]¶
Return type

Union[SerializedConstructor, SerializedNotImplemented]

to_json_not_implemented() SerializedNotImplemented¶
Return type

SerializedNotImplemented

classmethod update_forward_refs(**localns: Any) None¶

Try to update ForwardRefs on fields based on this Model, globalns and localns.

Parameters

localns (Any) –

Return type

None

classmethod validate(value: Any) Model¶
Parameters

value (Any) –

Return type

Model

property input_variables: List[str]¶

Input variables for this prompt template.

Returns

List of input variable names.

property lc_attributes: Dict¶

List of attribute names that should be included in the serialized kwargs.

These attributes must be accepted by the constructor.

property lc_secrets: Dict[str, str]¶

A map of constructor argument names to secret ids.

For example,

{“openai_api_key”: “OPENAI_API_KEY”}

Examples using MessagesPlaceholder¶