preprocessing/transformers.py

from sklearn.compose import ColumnTransformer
from sklearn.preprocessing import StandardScaler, OneHotEncoder

def build_preprocessor(X):
    num_cols = X.select_dtypes(include=["int64", "float64"]).columns
    cat_cols = X.select_dtypes(include=["object", "category"]).columns

    return ColumnTransformer(
        transformers=[
            ("num", StandardScaler(), num_cols),
            ("cat", OneHotEncoder(handle_unknown="ignore"), cat_cols),
        ]
    )