def err_ratio(predict, dataset, examples=None, verbose=0):
    """Return the proportion of the examples that are NOT correctly predicted.
    verbose - 0: No output; 1: Output wrong; 2 (or greater): Output correct"""
    if examples is None:
        examples = dataset.examples
    if len(examples) == 0:
        return 0.0
    right = 0.0
    for example in examples:
        desired = example[dataset.target]
        output = predict(dataset.sanitize(example))
        if output == desired:
            right += 1
            if verbose >= 2:
                print('   OK: got {} for {}'.format(desired, example))
        elif verbose:
            print('WRONG: got {}, expected {} for {}'.format(output,
                desired, example))
    return 1 - right / len(examples)
