def pad(value, return_type=str):
    """
        Pad binary value with zeros
        :param value: string
        :param return_type: string
    """
    if type(value) is not str:
        raise TypeError('pad only accepts str, not {}'.format(str(type(value)))
            )
    if len(value) % 4 != 0:
        pad_amount = 4 - len(value) % 4
        return return_type('0' * pad_amount + value)
    else:
        return return_type(value)
