Get bucket by length.

def get_buckets(min_length, max_length, bucket_count):
    '''
    Get bucket by length.
    '''
    if bucket_count <= 0:
        return [max_length]
    unit_length = int((max_length - min_length) // (bucket_count))
    buckets = [min_length + unit_length *
               (i + 1) for i in range(0, bucket_count)]
    buckets[-1] = max_length
    return buckets