microsoft/autogen · error · NotImplementedError

Subclasses must implement _from_config

Error message

Subclasses must implement _from_config

What it means

The base implementation of _from_config raises NotImplementedError('Subclasses must implement _from_config') for any subclass that was instantiated but did not override the abstract classmethod. It fires when a subclass somehow bypasses ABC enforcement (e.g. via the module's _allow_private_constructor ContextVar path) or a subclass was left incomplete.

Source

Thrown at python/packages/autogen-ext/src/autogen_ext/tools/azure/_ai_search.py:660

            if not vector_fields or len(vector_fields) == 0:
                raise ValueError("vector_fields must contain at least one field name for hybrid search")

            if not search_fields or len(search_fields) == 0:
                raise ValueError("search_fields must contain at least one field name for hybrid search")

    @classmethod
    @abstractmethod
    def _from_config(cls, config: AzureAISearchConfig) -> "BaseAzureAISearchTool":
        """Create a tool instance from a configuration object.

        This is an abstract method that must be implemented by subclasses.
        """
        if cls is BaseAzureAISearchTool:
            raise NotImplementedError(
                "BaseAzureAISearchTool is an abstract base class and cannot be instantiated directly. "
                "Use a concrete implementation like AzureAISearchTool."
            )
        raise NotImplementedError("Subclasses must implement _from_config")

    @abstractmethod
    async def _get_embedding(self, query: str) -> List[float]:
        """Generate embedding vector for the query text."""
        raise NotImplementedError("Subclasses must implement _get_embedding")


_allow_private_constructor = ContextVar("_allow_private_constructor", default=False)


class AzureAISearchTool(EmbeddingProviderMixin, BaseAzureAISearchTool):
    """Azure AI Search tool for querying Azure search indexes.

    This tool provides a simplified interface for querying Azure AI Search indexes using
    various search methods. It's recommended to use the factory methods to create
    instances tailored for specific search types:

    1.  **Full-Text Search**: For traditional keyword-based searches, Lucene queries, or

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Implement _from_config(cls, config: AzureAISearchConfig) -> Self in your subclass, constructing your instance from the config object.
2. Or inherit from the concrete AzureAISearchTool / EmbeddingProviderMixin stack instead of the raw base.
3. Run a quick isinstance/abstract check in tests: assert your class can be constructed normally (ABC will flag missing members at instantiation).

Example fix

# before
class MyTool(BaseAzureAISearchTool):
    ...
# after
class MyTool(BaseAzureAISearchTool):
    @classmethod
    def _from_config(cls, config: AzureAISearchConfig) -> 'MyTool':
        return cls(name=config.name, endpoint=config.endpoint, index_name=config.index_name, credential=config.credential)

def subclass_is_complete(cls) -> bool:
    from autogen_ext.tools.azure._ai_search import BaseAzureAISearchTool
    return issubclass(cls, BaseAzureAISearchTool) and '_from_config' in cls.__dict__

def implements_from_config(cls) -> bool:
    return any('_from_config' in vars(c) for c in cls.__mro__ if c is not object)

When it happens

Trigger: Defining a class inheriting BaseAzureAISearchTool without implementing _from_config, then constructing it through internal/private paths that skip abstractmethod checks; calling _from_config on such an incomplete subclass.

Common situations: Mid-way through writing a custom tool subclass and testing before all abstract members exist; copy-pasting a subclass template that omits _from_config.

Related errors

• BaseAzureAISearchTool is an abstract base class and cannot b
• Subclasses must implement _get_embedding
• Index '{self.search_config.index_name}' not found.
• Error from Azure AI Search: {error_msg}
• Invalid configuration: {str(e)}

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/a87982d60e040e1c. Report an issue: GitHub.