What causes "Unknown prompt_style='{prompt_style}'" in zylon-ai/private-gpt?

Use a registered builtin name: prompt_style='chat'.

zylon-ai/private-gpt · error · ValueError

Unknown prompt_style='{prompt_style}'

Error message

Unknown prompt_style='{prompt_style}'

What it means

PromptStyleRegistry.get_prompt_style looks the name up in the external factory dict (populated via register_prompt_style_factory) and then in the builtin dict, which currently contains only 'chat'. Any other string raises ValueError('Unknown prompt_style=...') because no factory is registered under that name.

Source

Thrown at private_gpt/components/llm/prompt_styles/registry.py:42


_BUILTIN_PROMPT_STYLE_FACTORIES: dict[str, PromptStyleProvider] = {
    "chat": _build_chat_template_prompt_style,
}


class PromptStyleRegistry:
    @staticmethod
    def get_prompt_style(
        prompt_style: str,
        *args: Any,
        **kwargs: Any,
    ) -> PromptStyleBase:
        factory = _EXTERNAL_PROMPT_STYLE_FACTORIES.get(
            prompt_style
        ) or _BUILTIN_PROMPT_STYLE_FACTORIES.get(prompt_style)
        if factory is None:
            raise ValueError(f"Unknown prompt_style='{prompt_style}'")
        return factory(*args, **kwargs)

View on GitHub (pinned to 4a030776a3)

Solutions

Use a registered builtin name: prompt_style='chat'.
Register your custom style before lookup: register_prompt_style_factory('my-style', MyPromptStyle).
Validate free-text config against the registry keys at startup so typos surface as config errors.

Example fix

// before
style = PromptStyleRegistry.get_prompt_style('default')

// after
from private_gpt.components.llm.prompt_styles.registry import register_prompt_style_factory
register_prompt_style_factory('my-style', MyPromptStyle)
style = PromptStyleRegistry.get_prompt_style('my-style', tokenizer=tok)

Defensive patterns

Strategy: validation

Validate before calling

from private_gpt.components.llm.prompt_styles import registry as ps_reg

def valid_prompt_style(name: str) -> bool:
    return name in ps_reg._EXTERNAL_PROMPT_STYLE_FACTORIES or name in ps_reg._BUILTIN_PROMPT_STYLE_FACTORIES

if not valid_prompt_style(config.prompt_style):
    raise ConfigurationError(f'prompt_style must be one of {ps_reg._BUILTIN_PROMPT_STYLE_FACTORIES.keys()} or a registered style')

Try / catch

try:
    style = PromptStyleRegistry.get_prompt_style(name, tokenizer=tok)
except ValueError as e:
    if 'Unknown prompt_style' in str(e):
        raise ConfigurationError(f'bad prompt_style: {name!r}') from e
    raise

Prevention

Validate prompt_style against the registry keys when loading settings.
Register custom styles once at import time in your app's entry module.
Treat style names as an enum in config rather than free text.

When it happens

Trigger: Calling PromptStyleRegistry.get_prompt_style('default') / get_prompt_style('Chat') / any typo or non-registered style name. Also occurs after renaming a style or when code assumes a style exists that was never registered via register_prompt_style_factory.

Common situations: Typo or casing mismatch ('Chat' vs 'chat'); upgrading to a version where previously available prompt styles were removed and only 'chat' remains; copy-pasting config from another project with extra styles without registering their factories.

Related errors

AI-assisted analysis of zylon-ai/private-gpt@4a030776a3 (2026-08-15). Data as JSON: /api/errors/1edc4c191658f689. Report an issue: GitHub.