import six


def zero_lpad(number, length):
    """
    Fill 0 on the left of number
    :param number: number to be padded
    :param length: length of result string
    :return:
    """
    if six.PY3:
        return str(number).ljust(length, '0')
    return '{number:0>{length}}'.format(number=number, length=length)