Config Objects

sklearn-genetic-opt groups advanced settings into four configuration objects. Passing None (the default) uses sensible defaults for each.

EvolutionConfig

Controls the core evolutionary algorithm parameters.

from sklearn_genetic import EvolutionConfig

EvolutionConfig(
    population_size=50,
    generations=80,
    crossover_probability=0.8,
    mutation_probability=0.1,
    tournament_size=3,
    elitism=True,
    keep_top_k=1,
    criteria="max",
    algorithm="eaMuPlusLambda",
)

Parameter	Type	Default	Description
population_size	int	50	Number of individuals per generation
generations	int	80	Number of generations to run
crossover_probability	float or adapter	0.8	Probability of crossover between two parents. Can be a fixed float or an adapter schedule
mutation_probability	float or adapter	0.1	Per-individual mutation probability. Can be a fixed float or an adapter schedule
tournament_size	int	3	Number of individuals competing in tournament selection
elitism	bool	True	Carry the best individual unchanged to the next generation
keep_top_k	int	1	Size of the hall of fame — best k individuals are preserved across generations
criteria	"max" or "min"	"max"	Whether to maximize or minimize the scoring metric
algorithm	str	"eaMuPlusLambda"	DEAP algorithm: "eaMuPlusLambda", "eaMuCommaLambda", or "eaSimple"

PopulationConfig

Controls how the initial population is created and seeded.

from sklearn_genetic import PopulationConfig

PopulationConfig(
    initializer="smart",
    warm_start_configs=None,
)

Parameter	Type	Default	Description
initializer	"smart" or "random"	"smart"	Population initialization strategy. "smart" uses Latin hypercube sampling, estimator defaults, stratified categoricals, and duplicate avoidance
warm_start_configs	list of dicts	None	Specific parameter configurations to include in the initial population. Each dict must have keys matching param_grid. Invalid configs are silently skipped

RuntimeConfig

Controls parallelism, caching, and runtime behavior.

from sklearn_genetic import RuntimeConfig

RuntimeConfig(
    n_jobs=None,
    pre_dispatch="2*n_jobs",
    error_score=np.nan,
    return_train_score=False,
    use_cache=True,
    parallel_backend="auto",
    verbose=True,
)

Parameter	Type	Default	Description
n_jobs	int or None	None	Number of parallel jobs. None = 1, -1 = all available cores
pre_dispatch	str or int	"2*n_jobs"	Number of jobs pre-dispatched for parallel execution
error_score	float or "raise"	np.nan	Score to assign when a candidate's fit raises an exception. Use "raise" to surface exceptions during debugging
return_train_score	bool	False	Include training scores in cv_results_
use_cache	bool	True	Cache evaluated candidates and reuse scores when the same configuration appears again
parallel_backend	str	"auto"	Parallelism strategy: "auto" or "population" (parallel across candidates in each generation), "cv" (parallel across CV folds within each candidate)
verbose	bool	True	Print the per-generation log during fit

Nested parallelism

If your estimator already uses parallelism (e.g., RandomForestClassifier(n_jobs=-1)), set parallel_backend="cv" or set the estimator's n_jobs=1 to avoid oversubscribing the CPU.

OptimizationConfig

Optional quality controls for the main GA loop. All features here are disabled by default except diversity_control.

from sklearn_genetic import OptimizationConfig

OptimizationConfig(
    # Diversity control (enabled by default)
    diversity_control=True,
    diversity_threshold=0.25,
    diversity_stagnation_generations=5,
    diversity_mutation_boost=2.0,
    random_immigrants_fraction=0.1,

    # Adaptive tournament selection
    adaptive_selection=False,
    selection_pressure_min=2,
    selection_pressure_max=None,
    offspring_diversity_retries=0,

    # Fitness sharing
    fitness_sharing=False,
    sharing_radius=0.2,
    sharing_alpha=1.0,

    # Local search
    local_search=False,
    local_search_top_k=1,
    local_search_steps=1,
    local_search_radius=0.1,

    # Final re-evaluation
    final_selection=False,
    final_selection_top_k=3,
    final_selection_cv=None,
)

Diversity Control

Parameter	Type	Default	Description
diversity_control	bool	True	Monitor population diversity and inject random immigrants when it drops below diversity_threshold
diversity_threshold	float	0.25	Genotype diversity level below which intervention triggers. Values 0.1–0.3 are typical
diversity_stagnation_generations	int	5	Also trigger diversity control after this many stagnant generations, even if diversity is above the threshold
diversity_mutation_boost	float	2.0	Multiplier applied to mutation_probability when diversity control triggers. Values 1.5–2.5 are typical
random_immigrants_fraction	float	0.1	Fraction of offspring replaced with random individuals when diversity control triggers

Adaptive Selection

Parameter	Type	Default	Description
adaptive_selection	bool	False	Adjust tournament size based on current diversity and stagnation
selection_pressure_min	int	2	Minimum tournament size when diversity is low
selection_pressure_max	int or None	None	Maximum tournament size. None uses tournament_size from EvolutionConfig
offspring_diversity_retries	int	0	Number of times to retry generating offspring that are distinct from parents

Fitness Sharing

Parameter	Type	Default	Description
fitness_sharing	bool	False	Apply niche-aware selection pressure: reduce the effective fitness of candidates that are too similar to each other
sharing_radius	float	0.2	Niche radius — normalized distance below which two individuals share fitness. Values 0.15–0.35 are typical
sharing_alpha	float	1.0	Sharing function exponent. Higher values narrow the sharing effect to very similar individuals

Local Search

Parameter	Type	Default	Description
local_search	bool	False	After the genetic search, evaluate neighbors of the top local_search_top_k hall-of-fame individuals
local_search_top_k	int	1	Number of hall-of-fame individuals to refine
local_search_steps	int	1	Number of neighbor evaluations per hall-of-fame individual. Each step adds cross-validation calls
local_search_radius	float	0.1	Step size as a fraction of the parameter range. Values 0.05–0.15 keep refinement local

Final Selection

Parameter	Type	Default	Description
final_selection	bool	False	Re-evaluate the top final_selection_top_k candidates after the GA and select the best before refitting
final_selection_top_k	int	3	Number of top candidates to re-evaluate
final_selection_cv	CV splitter or None	None	Cross-validation strategy for final selection. None reuses the main cv

See Also

• Advanced Optimizer Control — guide with worked examples
• Schedules — adaptive crossover/mutation rate schedules