import numpy as np

class DirectTransformer:
    """Utility for building class-like features from a single-point function, but that may need
    some general configuration first (you usually override __init__ for that)
    """

    def fit(self, X, y=None):
        return self

    def transform(self, X):
        return np.array([self.transform_one(x) for x in X]).reshape((-1, 1))

    def transform_one(self, x):
        raise NotImplementedError