Module answer_builder

AnswerBuilder

Converts a query and Generator replies into a GeneratedAnswer object.

AnswerBuilder parses Generator replies using custom regular expressions. Check out the usage example below to see how it works. Optionally, it can also take documents and metadata from the Generator to add to the GeneratedAnswer object. AnswerBuilder works with both non-chat and chat Generators.

Usage example

from haystack.components.builders import AnswerBuilder

builder = AnswerBuilder(pattern="Answer: (.*)")
builder.run(query="What's the answer?", replies=["This is an argument. Answer: This is the answer."])

AnswerBuilder.init

def __init__(pattern: Optional[str] = None,
             reference_pattern: Optional[str] = None)

Creates an instance of the AnswerBuilder component.

Arguments:

pattern: The regular expression pattern to extract the answer text from the Generator. If not specified, the entire response is used as the answer. The regular expression can have one capture group at most. If present, the capture group text is used as the answer. If no capture group is present, the whole match is used as the answer. Examples: [^\n]+$ finds "this is an answer" in a string "this is an argument.\nthis is an answer". Answer: (.*) finds "this is an answer" in a string "this is an argument. Answer: this is an answer".
reference_pattern: The regular expression pattern used for parsing the document references. If not specified, no parsing is done, and all documents are referenced. References need to be specified as indices of the input documents and start at [1]. Example: \[(\d+)\] finds "1" in a string "this is an answer[1]".

AnswerBuilder.run

@component.output_types(answers=List[GeneratedAnswer])
def run(query: str,
        replies: Union[List[str], List[ChatMessage]],
        meta: Optional[List[Dict[str, Any]]] = None,
        documents: Optional[List[Document]] = None,
        pattern: Optional[str] = None,
        reference_pattern: Optional[str] = None)

Turns the output of a Generator into GeneratedAnswer objects using regular expressions.

Arguments:

query: The input query used as the Generator prompt.
replies: The output of the Generator. Can be a list of strings or a list of ChatMessage objects.
meta: The metadata returned by the Generator. If not specified, the generated answer will contain no metadata.
documents: The documents used as the Generator inputs. If specified, they are added to theGeneratedAnswer objects. If both documents and reference_pattern are specified, the documents referenced in the Generator output are extracted from the input documents and added to the GeneratedAnswer objects.
pattern: The regular expression pattern to extract the answer text from the Generator. If not specified, the entire response is used as the answer. The regular expression can have one capture group at most. If present, the capture group text is used as the answer. If no capture group is present, the whole match is used as the answer. Examples: [^\n]+$ finds "this is an answer" in a string "this is an argument.\nthis is an answer". Answer: (.*) finds "this is an answer" in a string "this is an argument. Answer: this is an answer".
reference_pattern: The regular expression pattern used for parsing the document references. If not specified, no parsing is done, and all documents are referenced. References need to be specified as indices of the input documents and start at [1]. Example: \[(\d+)\] finds "1" in a string "this is an answer[1]".

Returns:

A dictionary with the following keys:

answers: The answers received from the output of the Generator.

Module prompt_builder

PromptBuilder

Renders a prompt filling in any variables so that it can send it to a Generator.

The prompt uses Jinja2 template syntax. The variables in the default template are used as PromptBuilder's input and are all optional. If they're not provided, they're replaced with an empty string in the rendered prompt. To try out different prompts, you can replace the prompt template at runtime by providing a template for each pipeline run invocation.

Usage examples

On its own

This example uses PromptBuilder to render a prompt template and fill it with target_language and snippet. PromptBuilder returns a prompt with the string "Translate the following context to Spanish. Context: I can't speak Spanish.; Translation:".

from haystack.components.builders import PromptBuilder

template = "Translate the following context to {{ target_language }}. Context: {{ snippet }}; Translation:"
builder = PromptBuilder(template=template)
builder.run(target_language="spanish", snippet="I can't speak spanish.")

In a Pipeline

This is an example of a RAG pipeline where PromptBuilder renders a custom prompt template and fills it with the contents of the retrieved documents and a query. The rendered prompt is then sent to a Generator.

from haystack import Pipeline, Document
from haystack.utils import Secret
from haystack.components.generators import OpenAIGenerator
from haystack.components.builders.prompt_builder import PromptBuilder

# in a real world use case documents could come from a retriever, web, or any other source
documents = [Document(content="Joe lives in Berlin"), Document(content="Joe is a software engineer")]
prompt_template = """
    Given these documents, answer the question.
    Documents:
    {% for doc in documents %}
        {{ doc.content }}
    {% endfor %}

    Question: {{query}}
    Answer:
    """
p = Pipeline()
p.add_component(instance=PromptBuilder(template=prompt_template), name="prompt_builder")
p.add_component(instance=OpenAIGenerator(api_key=Secret.from_env_var("OPENAI_API_KEY")), name="llm")
p.connect("prompt_builder", "llm")

question = "Where does Joe live?"
result = p.run({"prompt_builder": {"documents": documents, "query": question}})
print(result)

Changing the template at runtime (prompt engineering)

You can change the prompt template of an existing pipeline, like in this example:

documents = [
    Document(content="Joe lives in Berlin", meta={"name": "doc1"}),
    Document(content="Joe is a software engineer", meta={"name": "doc1"}),
]
new_template = """
    You are a helpful assistant.
    Given these documents, answer the question.
    Documents:
    {% for doc in documents %}
        Document {{ loop.index }}:
        Document name: {{ doc.meta['name'] }}
        {{ doc.content }}
    {% endfor %}

    Question: {{ query }}
    Answer:
    """
p.run({
    "prompt_builder": {
        "documents": documents,
        "query": question,
        "template": new_template,
    },
})

To replace the variables in the default template when testing your prompt, pass the new variables in the variables parameter.

Overwriting variables at runtime

To overwrite the values of variables, use template_variables during runtime:

language_template = """
You are a helpful assistant.
Given these documents, answer the question.
Documents:
{% for doc in documents %}
    Document {{ loop.index }}:
    Document name: {{ doc.meta['name'] }}
    {{ doc.content }}
{% endfor %}

Question: {{ query }}
Please provide your answer in {{ answer_language | default('English') }}
Answer:
"""
p.run({
    "prompt_builder": {
        "documents": documents,
        "query": question,
        "template": language_template,
        "template_variables": {"answer_language": "German"},
    },
})

Note that language_template introduces variable answer_language which is not bound to any pipeline variable. If not set otherwise, it will use its default value 'English'. This example overwrites its value to 'German'. Use template_variables to overwrite pipeline variables (such as documents) as well.

PromptBuilder.init

def __init__(template: str,
             required_variables: Optional[Union[List[str],
                                                Literal["*"]]] = None,
             variables: Optional[List[str]] = None)

Constructs a PromptBuilder component.

Arguments:

template: A prompt template that uses Jinja2 syntax to add variables. For example: "Summarize this document: {{ documents[0].content }}\nSummary:" It's used to render the prompt. The variables in the default template are input for PromptBuilder and are all optional, unless explicitly specified. If an optional variable is not provided, it's replaced with an empty string in the rendered prompt.
required_variables: List variables that must be provided as input to PromptBuilder. If a variable listed as required is not provided, an exception is raised. If set to "*", all variables found in the prompt are required. Optional.
variables: List input variables to use in prompt templates instead of the ones inferred from the template parameter. For example, to use more variables during prompt engineering than the ones present in the default template, you can provide them here.

PromptBuilder.to_dict

def to_dict() -> Dict[str, Any]

Returns a dictionary representation of the component.

Returns:

Serialized dictionary representation of the component.

PromptBuilder.run

@component.output_types(prompt=str)
def run(template: Optional[str] = None,
        template_variables: Optional[Dict[str, Any]] = None,
        **kwargs)

Renders the prompt template with the provided variables.

It applies the template variables to render the final prompt. You can provide variables via pipeline kwargs. In order to overwrite the default template, you can set the template parameter. In order to overwrite pipeline kwargs, you can set the template_variables parameter.

Arguments:

template: An optional string template to overwrite PromptBuilder's default template. If None, the default template provided at initialization is used.
template_variables: An optional dictionary of template variables to overwrite the pipeline variables.
kwargs: Pipeline variables used for rendering the prompt.

Raises:

ValueError: If any of the required template variables is not provided.

Returns:

A dictionary with the following keys:

prompt: The updated prompt text after rendering the prompt template.

Module chat_prompt_builder

ChatPromptBuilder

Renders a chat prompt from a template string using Jinja2 syntax.

It constructs prompts using static or dynamic templates, which you can update for each pipeline run.

Template variables in the template are optional unless specified otherwise. If an optional variable isn't provided, it defaults to an empty string. Use variable and required_variables to define input types and required variables.

Usage examples

With static prompt template

template = [ChatMessage.from_user("Translate to {{ target_language }}. Context: {{ snippet }}; Translation:")]
builder = ChatPromptBuilder(template=template)
builder.run(target_language="spanish", snippet="I can't speak spanish.")

Overriding static template at runtime

template = [ChatMessage.from_user("Translate to {{ target_language }}. Context: {{ snippet }}; Translation:")]
builder = ChatPromptBuilder(template=template)
builder.run(target_language="spanish", snippet="I can't speak spanish.")

msg = "Translate to {{ target_language }} and summarize. Context: {{ snippet }}; Summary:"
summary_template = [ChatMessage.from_user(msg)]
builder.run(target_language="spanish", snippet="I can't speak spanish.", template=summary_template)

With dynamic prompt template

from haystack.components.builders import ChatPromptBuilder
from haystack.components.generators.chat import OpenAIChatGenerator
from haystack.dataclasses import ChatMessage
from haystack import Pipeline
from haystack.utils import Secret

# no parameter init, we don't use any runtime template variables
prompt_builder = ChatPromptBuilder()
llm = OpenAIChatGenerator(api_key=Secret.from_token("<your-api-key>"), model="gpt-4o-mini")

pipe = Pipeline()
pipe.add_component("prompt_builder", prompt_builder)
pipe.add_component("llm", llm)
pipe.connect("prompt_builder.prompt", "llm.messages")

location = "Berlin"
language = "English"
system_message = ChatMessage.from_system("You are an assistant giving information to tourists in {{language}}")
messages = [system_message, ChatMessage.from_user("Tell me about {{location}}")]

res = pipe.run(data={"prompt_builder": {"template_variables": {"location": location, "language": language},
                                    "template": messages}})
print(res)

>> {'llm': {'replies': [ChatMessage(content="Berlin is the capital city of Germany and one of the most vibrant
and diverse cities in Europe. Here are some key things to know...Enjoy your time exploring the vibrant and dynamic
capital of Germany!", role=<ChatRole.ASSISTANT: 'assistant'>, name=None, meta={'model': 'gpt-4o-mini',
'index': 0, 'finish_reason': 'stop', 'usage': {'prompt_tokens': 27, 'completion_tokens': 681, 'total_tokens':
708}})]}}


messages = [system_message, ChatMessage.from_user("What's the weather forecast for {{location}} in the next
{{day_count}} days?")]

res = pipe.run(data={"prompt_builder": {"template_variables": {"location": location, "day_count": "5"},
                                    "template": messages}})

print(res)
>> {'llm': {'replies': [ChatMessage(content="Here is the weather forecast for Berlin in the next 5
days:\n\nDay 1: Mostly cloudy with a high of 22°C (72°F) and...so it's always a good idea to check for updates
closer to your visit.", role=<ChatRole.ASSISTANT: 'assistant'>, name=None, meta={'model': 'gpt-4o-mini',
'index': 0, 'finish_reason': 'stop', 'usage': {'prompt_tokens': 37, 'completion_tokens': 201,
'total_tokens': 238}})]}}

ChatPromptBuilder.init

def __init__(template: Optional[List[ChatMessage]] = None,
             required_variables: Optional[Union[List[str],
                                                Literal["*"]]] = None,
             variables: Optional[List[str]] = None)

Constructs a ChatPromptBuilder component.

Arguments:

template: A list of ChatMessage objects. The component looks for Jinja2 template syntax and renders the prompt with the provided variables. Provide the template in either the init methodor therun` method.
required_variables: List variables that must be provided as input to ChatPromptBuilder. If a variable listed as required is not provided, an exception is raised. If set to "*", all variables found in the prompt are required. Optional.
variables: List input variables to use in prompt templates instead of the ones inferred from the template parameter. For example, to use more variables during prompt engineering than the ones present in the default template, you can provide them here.

ChatPromptBuilder.run

@component.output_types(prompt=List[ChatMessage])
def run(template: Optional[List[ChatMessage]] = None,
        template_variables: Optional[Dict[str, Any]] = None,
        **kwargs)

Renders the prompt template with the provided variables.

It applies the template variables to render the final prompt. You can provide variables with pipeline kwargs. To overwrite the default template, you can set the template parameter. To overwrite pipeline kwargs, you can set the template_variables parameter.

Arguments:

template: An optional list of ChatMessage objects to overwrite ChatPromptBuilder's default template. If None, the default template provided at initialization is used.
template_variables: An optional dictionary of template variables to overwrite the pipeline variables.
kwargs: Pipeline variables used for rendering the prompt.

Raises:

ValueError: If chat_messages is empty or contains elements that are not instances of ChatMessage.

Returns:

A dictionary with the following keys:

prompt: The updated list of ChatMessage objects after rendering the templates.

ChatPromptBuilder.to_dict

def to_dict() -> Dict[str, Any]

Returns a dictionary representation of the component.

Returns:

Serialized dictionary representation of the component.

ChatPromptBuilder.from_dict

@classmethod
def from_dict(cls, data: Dict[str, Any]) -> "ChatPromptBuilder"

Deserialize this component from a dictionary.

Arguments:

data: The dictionary to deserialize and create the component.

Returns:

The deserialized component.

Module answer_builder

AnswerBuilder

Usage example

AnswerBuilder.__init__

AnswerBuilder.run

Module prompt_builder

PromptBuilder

Usage examples

On its own

In a Pipeline

Changing the template at runtime (prompt engineering)

Overwriting variables at runtime

PromptBuilder.__init__

PromptBuilder.to_dict

PromptBuilder.run

Module chat_prompt_builder

ChatPromptBuilder

Usage examples

With static prompt template

Overriding static template at runtime

With dynamic prompt template

ChatPromptBuilder.__init__

ChatPromptBuilder.run

ChatPromptBuilder.to_dict

ChatPromptBuilder.from_dict

AnswerBuilder.init

PromptBuilder.init

ChatPromptBuilder.init