def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
def balanced_accuracy_scoring(clf, X, y):
    """Scoring function that computes the balanced accuracy to be used
    internally in the cross-validation procedure.
    """
    y_pred = clf.predict(X)
    conf_mat = confusion_matrix(y, y_pred)
    bal_acc = 0.
    for i in range(len(conf_mat)):
        bal_acc += (float(conf_mat[i, i])) / np.sum(conf_mat[i])

    bal_acc /= len(conf_mat)
    return bal_acc