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Component selector

component_selector

Adapter implementations for component selection strategies.

This module provides concrete implementations of the ComponentSelectorProtocol, allowing different strategies for selecting which components of a candidate to update during evolution.

ATTRIBUTE DESCRIPTION
RoundRobinComponentSelector

Cycles through components sequentially. Defined in gepa_adk.ports.defaults and re-exported here.

TYPE: class

AllComponentSelector

Selects all components every time.

TYPE: class

create_component_selector

Create a component selector strategy from a string alias.

TYPE: function

Examples:

Creating a selector via factory:

from gepa_adk.adapters.selection.component_selector import create_component_selector

selector = create_component_selector("round_robin")

Using a selector directly:

from gepa_adk.adapters.selection.component_selector import AllComponentSelector

selector = AllComponentSelector()
components = await selector.select_components(["a", "b"], 1, 0)
See Also
Notes

RoundRobinComponentSelector is the engine's default, so it lives beside its protocol in gepa_adk.ports.defaults, where both the engine and the adapters may import it under ADR-000; this module re-exports it so its import path and isinstance checks keep working.

These adapters implement component selection strategies that may maintain internal state for cycling (like RoundRobin) while remaining stateless with respect to the engine.

RoundRobinComponentSelector

Selects components in a round-robin fashion.

This selector cycles through the list of components one by one, maintaining state per candidate index to ensure consistent rotation.

ATTRIBUTE DESCRIPTION
_next_index

Mapping of candidate_idx to next component index.

TYPE: dict[int, int]

Examples:

selector = RoundRobinComponentSelector()
# First call selects first component
c1 = await selector.select_components(["a", "b"], 1, 0)  # ["a"]
# Second call selects second component
c2 = await selector.select_components(["a", "b"], 2, 0)  # ["b"]
Notes

Alternates through components sequentially, ensuring balanced evolution across all candidate parts.

Source code in src/gepa_adk/ports/defaults.py 
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class RoundRobinComponentSelector:
    """Selects components in a round-robin fashion.

    This selector cycles through the list of components one by one, maintaining
    state per candidate index to ensure consistent rotation.

    Attributes:
        _next_index (dict[int, int]): Mapping of candidate_idx to next component index.

    Examples:
        ```python
        selector = RoundRobinComponentSelector()
        # First call selects first component
        c1 = await selector.select_components(["a", "b"], 1, 0)  # ["a"]
        # Second call selects second component
        c2 = await selector.select_components(["a", "b"], 2, 0)  # ["b"]
        ```

    Notes:
        Alternates through components sequentially, ensuring balanced evolution
        across all candidate parts.
    """

    def __init__(self) -> None:
        """Initialize the round-robin selector.

        Notes:
            Creates empty index tracking dictionary for per-candidate rotation state.
        """
        self._next_index: dict[int, int] = defaultdict(int)

    async def select_components(
        self, components: list[str], iteration: int, candidate_idx: int
    ) -> list[str]:
        """Select a single component to update using round-robin logic.

        Args:
            components: List of available component keys.
            iteration: Current global iteration number (unused by this strategy).
            candidate_idx: Index of the candidate being evolved.

        Returns:
            List containing the single selected component key.

        Raises:
            ValueError: If components list is empty.

        Examples:
            ```python
            selected = await selector.select_components(["a", "b"], 1, 0)
            ```

        Notes:
            Outputs one component per call, advancing the rotation index for
            the specified candidate.
        """
        if not components:
            raise ValueError("No components provided for selection")

        # Get current index for this candidate
        current_idx = self._next_index[candidate_idx]

        # Select component
        selected = components[current_idx % len(components)]

        # Advance index for next time
        self._next_index[candidate_idx] = (current_idx + 1) % len(components)

        return [selected]

__init__ 

__init__() -> None

Initialize the round-robin selector.

Notes

Creates empty index tracking dictionary for per-candidate rotation state.

Source code in src/gepa_adk/ports/defaults.py 
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def __init__(self) -> None:
    """Initialize the round-robin selector.

    Notes:
        Creates empty index tracking dictionary for per-candidate rotation state.
    """
    self._next_index: dict[int, int] = defaultdict(int)

select_components async 

select_components(
    components: list[str],
    iteration: int,
    candidate_idx: int,
) -> list[str]

Select a single component to update using round-robin logic.

PARAMETER DESCRIPTION
components

List of available component keys.

TYPE: list[str]

iteration

Current global iteration number (unused by this strategy).

TYPE: int

candidate_idx

Index of the candidate being evolved.

TYPE: int

RETURNS DESCRIPTION
list[str]

List containing the single selected component key.
RAISES DESCRIPTION
ValueError

If components list is empty.

Examples:

selected = await selector.select_components(["a", "b"], 1, 0)
Notes

Outputs one component per call, advancing the rotation index for the specified candidate.

Source code in src/gepa_adk/ports/defaults.py 
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async def select_components(
    self, components: list[str], iteration: int, candidate_idx: int
) -> list[str]:
    """Select a single component to update using round-robin logic.

    Args:
        components: List of available component keys.
        iteration: Current global iteration number (unused by this strategy).
        candidate_idx: Index of the candidate being evolved.

    Returns:
        List containing the single selected component key.

    Raises:
        ValueError: If components list is empty.

    Examples:
        ```python
        selected = await selector.select_components(["a", "b"], 1, 0)
        ```

    Notes:
        Outputs one component per call, advancing the rotation index for
        the specified candidate.
    """
    if not components:
        raise ValueError("No components provided for selection")

    # Get current index for this candidate
    current_idx = self._next_index[candidate_idx]

    # Select component
    selected = components[current_idx % len(components)]

    # Advance index for next time
    self._next_index[candidate_idx] = (current_idx + 1) % len(components)

    return [selected]

AllComponentSelector

Selects all available components for simultaneous update.

This selector returns the full list of components every time, enabling simultaneous evolution of all parts of the candidate.

Examples:

selector = AllComponentSelector()
all_comps = await selector.select_components(["a", "b"], 1, 0)
# Returns ["a", "b"]
Notes

Always returns all components, enabling comprehensive mutations across the entire candidate in a single iteration.

Source code in src/gepa_adk/adapters/selection/component_selector.py 
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class AllComponentSelector:
    """Selects all available components for simultaneous update.

    This selector returns the full list of components every time, enabling
    simultaneous evolution of all parts of the candidate.

    Examples:
        ```python
        selector = AllComponentSelector()
        all_comps = await selector.select_components(["a", "b"], 1, 0)
        # Returns ["a", "b"]
        ```

    Notes:
        Always returns all components, enabling comprehensive mutations
        across the entire candidate in a single iteration.
    """

    async def select_components(
        self, components: list[str], iteration: int, candidate_idx: int
    ) -> list[str]:
        """Select all components to update.

        Args:
            components: List of available component keys.
            iteration: Current global iteration number (unused).
            candidate_idx: Index of the candidate being evolved (unused).

        Returns:
            List containing all component keys.

        Raises:
            ValueError: If components list is empty.

        Examples:
            ```python
            selected = await selector.select_components(["a", "b"], 1, 0)
            ```

        Notes:
            Outputs the complete component list unchanged, enabling
            simultaneous evolution of all candidate parts.
        """
        if not components:
            raise ValueError("No components provided for selection")

        return list(components)

select_components async 

select_components(
    components: list[str],
    iteration: int,
    candidate_idx: int,
) -> list[str]

Select all components to update.

PARAMETER DESCRIPTION
components

List of available component keys.

TYPE: list[str]

iteration

Current global iteration number (unused).

TYPE: int

candidate_idx

Index of the candidate being evolved (unused).

TYPE: int

RETURNS DESCRIPTION
list[str]

List containing all component keys.
RAISES DESCRIPTION
ValueError

If components list is empty.

Examples:

selected = await selector.select_components(["a", "b"], 1, 0)
Notes

Outputs the complete component list unchanged, enabling simultaneous evolution of all candidate parts.

Source code in src/gepa_adk/adapters/selection/component_selector.py 
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async def select_components(
    self, components: list[str], iteration: int, candidate_idx: int
) -> list[str]:
    """Select all components to update.

    Args:
        components: List of available component keys.
        iteration: Current global iteration number (unused).
        candidate_idx: Index of the candidate being evolved (unused).

    Returns:
        List containing all component keys.

    Raises:
        ValueError: If components list is empty.

    Examples:
        ```python
        selected = await selector.select_components(["a", "b"], 1, 0)
        ```

    Notes:
        Outputs the complete component list unchanged, enabling
        simultaneous evolution of all candidate parts.
    """
    if not components:
        raise ValueError("No components provided for selection")

    return list(components)

create_component_selector 

create_component_selector(
    selector_type: str,
) -> ComponentSelectorProtocol

Create a component selector strategy from a string alias.

PARAMETER DESCRIPTION
selector_type

Name of the selector strategy. Supported values: - 'round_robin', 'roundrobin': Round-robin cycling. - 'all', 'all_components': All components simultaneously.

TYPE: str

RETURNS DESCRIPTION
ComponentSelectorProtocol

Instance of requested component selector.
RAISES DESCRIPTION
ValueError

If selector_type is unknown.

Examples:

# Create round-robin selector
selector = create_component_selector("round_robin")

# Create all-components selector
selector = create_component_selector("all")
Notes

Supports flexible string aliases with normalization for common variations (underscores, hyphens, case-insensitive).

Source code in src/gepa_adk/adapters/selection/component_selector.py 
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def create_component_selector(selector_type: str) -> ComponentSelectorProtocol:
    """Create a component selector strategy from a string alias.

    Args:
        selector_type: Name of the selector strategy.
            Supported values:
            - 'round_robin', 'roundrobin': Round-robin cycling.
            - 'all', 'all_components': All components simultaneously.

    Returns:
        Instance of requested component selector.

    Raises:
        ValueError: If selector_type is unknown.

    Examples:
        ```python
        # Create round-robin selector
        selector = create_component_selector("round_robin")

        # Create all-components selector
        selector = create_component_selector("all")
        ```

    Notes:
        Supports flexible string aliases with normalization for common
        variations (underscores, hyphens, case-insensitive).
    """
    normalized = selector_type.lower().replace("_", "").replace("-", "")

    if normalized == "roundrobin":
        return RoundRobinComponentSelector()
    elif normalized in ("all", "allcomponents"):
        return AllComponentSelector()

    raise ValueError(f"Unknown component selector: {selector_type}")