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Reproducibility

Genetic algorithms are stochastic — results vary between runs unless the randomness is seeded. The simplest, recommended way is the single random_state parameter on GASearchCV / GAFeatureSelectionCV.

Prerequisites

• Completed Basic Usage

One Seed Controls the Search

Pass random_state to the estimator. At fit time it seeds every stochastic part of the search from that one value — population initialization (including the Latin hypercube sampler), mutation, crossover, and random immigrants — so repeated fits give identical results. You no longer need to seed the global random / numpy RNGs yourself.

from sklearn.datasets import load_breast_cancer
from sklearn.ensemble import RandomForestClassifier
from sklearn.model_selection import StratifiedKFold, train_test_split

from sklearn_genetic import EvolutionConfig, GASearchCV, PopulationConfig, RuntimeConfig
from sklearn_genetic.space import Categorical, Continuous, Integer

X, y = load_breast_cancer(return_X_y=True)
X_train, X_test, y_train, y_test = train_test_split(
    X, y, test_size=0.25, stratify=y, random_state=42  # seed the split
)

search = GASearchCV(
    estimator=RandomForestClassifier(random_state=42),  # seed the estimator
    random_state=42,                                    # seed the whole search
    param_grid={
        "n_estimators": Integer(50, 250),
        "max_depth": Integer(2, 14),
        "max_features": Categorical(["sqrt", "log2"]),
        "ccp_alpha": Continuous(0.0, 0.03),
    },
    cv=StratifiedKFold(n_splits=3, shuffle=True, random_state=42),  # seed CV
    scoring="roc_auc",
    evolution_config=EvolutionConfig(population_size=20, generations=12),
    population_config=PopulationConfig(initializer="smart"),
    runtime_config=RuntimeConfig(n_jobs=1),  # n_jobs=1 for full determinism
)

search.fit(X_train, y_train)

The four random_state=42 values above seed four independent things: the train/test split, the estimator, the cross-validation splitter, and — the new one — the genetic search itself. Set all four for an end-to-end reproducible run.

Leave it unset for variety

random_state=None (the default) keeps the search non-deterministic, matching scikit-learn's convention — useful when you want to explore different runs.

Why n_jobs=1?

Parallel execution with n_jobs > 1 uses joblib, which may introduce non-determinism when multiple workers race to write results. For fully reproducible results, use n_jobs=1. For production runs where speed matters, accept that results may vary slightly between runs.

Checkpointing

For long runs, save the logbook periodically so you can inspect progress even if the search is interrupted:

from sklearn_genetic.callbacks import LogbookSaver

search.fit(X_train, y_train, callbacks=[
    LogbookSaver(checkpoint_path="./logbook.pkl")
])

# Load later:
import pickle
with open("./logbook.pkl", "rb") as f:
    logbook = pickle.load(f)

Tips & Gotchas

• Seed random, np.random, the CV splitter, and every estimator that accepts random_state.
• If using PopulationConfig(warm_start_configs=[...]), the warm-start configs are deterministic by definition.
• DEAP's internal RNG is seeded through Python's random module — seeding random before fit is sufficient.

Next Steps

• Troubleshooting — debugging non-deterministic results.
• Callbacks — use LogbookSaver for checkpointing.