microsoft/semantic-kernel · error · ServiceInitializationError

Values for filter key '{key}' are not lists.

Error message

Values for filter key '{key}' are not lists.

What it means

Raised by the internal _combine_filter_dicts helper when merging function-choice filter dictionaries: it expects every value to be a list of strings, but encountered a non-list value for a given key. The helper unions filter keys across dicts and deduplicates list entries, so a scalar value cannot be merged.

Source

Thrown at python/semantic_kernel/connectors/ai/function_calling_utils.py:97

def _combine_filter_dicts(*dicts: dict[str, list[str]]) -> dict:
    """Combine multiple filter dictionaries with list values into one dictionary.

    This method is ensuring unique values while preserving order.
    """
    combined_filters = {}

    keys = set().union(*(d.keys() for d in dicts))

    for key in keys:
        combined_functions: OrderedDict[str, None] = OrderedDict()
        for d in dicts:
            if key in d:
                if isinstance(d[key], list):
                    for item in d[key]:
                        combined_functions[item] = None
                else:
                    raise ServiceInitializationError(f"Values for filter key '{key}' are not lists.")
        combined_filters[key] = list(combined_functions.keys())

    return combined_filters


def merge_function_results(
    messages: list["ChatMessageContent"],
) -> list["ChatMessageContent"]:
    """Combine multiple function result content types to one chat message content type.

    This method combines the FunctionResultContent items from separate ChatMessageContent messages,
    and is used in the event that the `context.terminate = True` condition is met.
    """
    from semantic_kernel.contents.chat_message_content import ChatMessageContent
    from semantic_kernel.contents.function_result_content import FunctionResultContent

    items: list[Any] = []
    for message in messages:

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Ensure every filter value is a list of strings, e.g. {'included_functions': ['plugin-function']}.
2. Normalize scalar inputs to single-element lists before calling FunctionChoiceBehavior.from_dict.
3. Validate the filters dict shape before constructing the behavior.

Example fix

# before
filters = {"included_functions": "search-web"}
behavior = FunctionChoiceBehavior.from_dict({"type": "auto", "filters": filters})
# after
filters = {"included_functions": ["search-web"]}
behavior = FunctionChoiceBehavior.from_dict({"type": "auto", "filters": filters})

def filters_values_are_lists(filters: dict) -> bool:
    return all(isinstance(v, list) and all(isinstance(x, str) for x in v) for v in filters.values())

from typing import Any

def is_valid_filter_dict(filters: Any) -> bool:
    return isinstance(filters, dict) and all(isinstance(v, list) for v in filters.values())

from semantic_kernel.exceptions.service_exceptions import ServiceInitializationError

try:
    behavior = FunctionChoiceBehavior.from_dict({"type": "auto", "filters": filters})
except ServiceInitializationError as e:
    if "are not lists" in str(e):
        filters = {k: ([v] if isinstance(v, str) else v) for k, v in filters.items()}
        behavior = FunctionChoiceBehavior.from_dict({"type": "auto", "filters": filters})
    else:
        raise

When it happens

Trigger: FunctionChoiceBehavior.from_dict or any caller of _combine_filter_dicts passing filter dicts whose values are not lists, e.g. {'included_functions': 'my-func'} instead of {'included_functions': ['my-func']}.

Common situations: Hand-building a filters dict with scalar values; deserializing a config/YAML where a single function name was given as a string rather than a one-element list; merging a user-supplied filters dict that did not validate shapes.

Related errors

• The specified type `{type_value}` is not supported. Allowed
• Invalid kernel selection. {selectedKernelName} is not a vali
• Azure AI Search tool definition must have both 'index_connec
• The option keys 'asset_identifiers' and 'asset_type' are req
• The option keys 'store_name' and 'data_sources' are required

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/8ae7c985613665a5. Report an issue: GitHub.