def zeroPrepender(source, length):
    """
    Append extra zeros to a source number based on the specified length
    """
    if (not source and source != 0) or not length:
        return None

    result = str(source)
    if len(result) >= length:
        return result

    for i in range(length - len(result)):
        result = '0' + result

    return result