Class PromptTemplate<RunInput, PartialVariableName>

Schema to represent a basic prompt for an LLM.

Example

import { PromptTemplate } from "langchain/prompts";

const prompt = new PromptTemplate({
inputVariables: ["foo"],
template: "Say {foo}",
});

Type Parameters

  • RunInput extends InputValues = any

  • PartialVariableName extends string = any

Hierarchy

Implements

Constructors

Properties

PromptValueReturnType: StringPromptValue
inputVariables: Extract<keyof RunInput, string>[]

A list of variable names the prompt template expects

partialVariables: PartialValues<PartialVariableName>

Partial variables

template: string

The prompt template

templateFormat: "f-string"

The format of the prompt template. Options are 'f-string'

Default Value

'f-string'

validateTemplate: boolean

Whether or not to try validating the template on initialization

Default Value

true

outputParser?: BaseOutputParser<unknown>

How to parse the output of calling an LLM on this formatted prompt

Methods

  • Formats the prompt template with the provided values.

    Parameters

    • values: TypedPromptInputValues<RunInput>

      The values to be used to format the prompt template.

    Returns Promise<string>

    A promise that resolves to a string which is the formatted prompt.

  • Formats the prompt given the input values and returns a formatted prompt value.

    Parameters

    • values: TypedPromptInputValues<RunInput>

      The input values to format the prompt.

    Returns Promise<StringPromptValue>

    A Promise that resolves to a formatted prompt value.

  • Invokes the prompt template with the given input and options.

    Parameters

    • input: RunInput

      The input to invoke the prompt template with.

    • Optional options: BaseCallbackConfig

      Optional configuration for the callback.

    Returns Promise<StringPromptValue>

    A Promise that resolves to the output of the prompt template.

  • Merges partial variables and user variables.

    Parameters

    • userVariables: TypedPromptInputValues<RunInput>

      The user variables to merge with the partial variables.

    Returns Promise<InputValues<PartialVariableName | Extract<keyof RunInput, string>>>

    A Promise that resolves to an object containing the merged variables.

  • Partially applies values to the prompt template.

    Type Parameters

    • NewPartialVariableName extends string

    Parameters

    • values: PartialValues<NewPartialVariableName>

      The values to be partially applied to the prompt template.

    Returns Promise<PromptTemplate<InputValues<Exclude<Extract<keyof RunInput, string>, NewPartialVariableName>>, any>>

    A new instance of PromptTemplate with the partially applied values.

  • Create a new runnable sequence that runs each individual runnable in series, piping the output of one runnable into another runnable or runnable-like.

    Type Parameters

    • NewRunOutput

    Parameters

    Returns RunnableSequence<RunInput, Exclude<NewRunOutput, Error>>

    A new runnable sequence.

  • Stream all output from a runnable, as reported to the callback system. This includes all inner runs of LLMs, Retrievers, Tools, etc. Output is streamed as Log objects, which include a list of jsonpatch ops that describe how the state of the run has changed in each step, and the final state of the run. The jsonpatch ops can be applied in order to construct state.

    Parameters

    • input: RunInput
    • Optional options: Partial<BaseCallbackConfig>
    • Optional streamOptions: Omit<LogStreamCallbackHandlerInput, "autoClose">

    Returns AsyncGenerator<RunLogPatch, any, unknown>

  • Default implementation of transform, which buffers input and then calls stream. Subclasses should override this method if they can start producing output while input is still being generated.

    Parameters

    Returns AsyncGenerator<StringPromptValue, any, unknown>

  • Bind lifecycle listeners to a Runnable, returning a new Runnable. The Run object contains information about the run, including its id, type, input, output, error, startTime, endTime, and any tags or metadata added to the run.

    Parameters

    • params: {
          onEnd?: ((run, config?) => void | Promise<void>);
          onError?: ((run, config?) => void | Promise<void>);
          onStart?: ((run, config?) => void | Promise<void>);
      }

      The object containing the callback functions.

      • Optional onEnd?: ((run, config?) => void | Promise<void>)
          • (run, config?): void | Promise<void>
          • Called after the runnable finishes running, with the Run object.

            Parameters

            Returns void | Promise<void>

      • Optional onError?: ((run, config?) => void | Promise<void>)
          • (run, config?): void | Promise<void>
          • Called if the runnable throws an error, with the Run object.

            Parameters

            Returns void | Promise<void>

      • Optional onStart?: ((run, config?) => void | Promise<void>)
          • (run, config?): void | Promise<void>
          • Called before the runnable starts running, with the Run object.

            Parameters

            Returns void | Promise<void>

    Returns Runnable<RunInput, StringPromptValue, BaseCallbackConfig>

  • Take examples in list format with prefix and suffix to create a prompt.

    Intended to be used a a way to dynamically create a prompt from examples.

    Parameters

    • examples: string[]

      List of examples to use in the prompt.

    • suffix: string

      String to go after the list of examples. Should generally set up the user's input.

    • inputVariables: string[]

      A list of variable names the final prompt template will expect

    • Optional exampleSeparator: string

      The separator to use in between examples

    • Optional prefix: string

      String that should go before any examples. Generally includes examples.

    Returns PromptTemplate<any, any>

    The final prompt template generated.

  • Load prompt template from a template f-string

    Type Parameters

    • RunInput extends InputValues = Symbol

    • T extends string = string

    Parameters

    • template: T
    • Optional __namedParameters: Omit<PromptTemplateInput<RunInput, string>, "inputVariables" | "template">

    Returns PromptTemplate<RunInput extends Symbol
        ? ParamsFromFString<T>
        : RunInput, any>

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