def listPrinters(self):
     printers = core.find(find_all=True)  # , bDeviceClass=7)
     for printer in printers:
         print printer.bDeviceClass
         try:
             print util.get_string(printer, 256, 3)
         except:
             print 'dispositivo oculto'

def _try_get_string(dev, index, langid = None, default_str_i0 = "",
        default_access_error = "Error Accessing String"):
    """ try to get a string, but return a string no matter what
    """
    if index == 0 :
        string = default_str_i0
    else:
        try:
            if langid is None:
                string = util.get_string(dev, index)
            else:
                string = util.get_string(dev, index, langid)
        except :
            string = default_access_error
    return string

    def manufacturer(self):
        """ Return the USB device's manufacturer string descriptor.

        This property will cause some USB traffic the first time it is accessed
        and cache the resulting value for future use.
        """
        if self._manufacturer is None:
            self._manufacturer = util.get_string(self, self.iManufacturer)
        return self._manufacturer

    def product(self):
        """ Return the USB device's product string descriptor.

        This property will cause some USB traffic the first time it is accessed
        and cache the resulting value for future use.
        """
        if self._product is None:
            self._product = util.get_string(self, self.iProduct)
        return self._product

    def serial_number(self):
        """ Return the USB device's serial number string descriptor

        This property will cause some USB traffic the first time it is accessed
        and cache the resulting value for future use.
        """
        if self._serial_number is None:
            self._serial_number = util.get_string(self, self.iSerialNumber)
        return self._serial_number

    def getString(self, index, length, langid = None):
        r"""Retrieve the string descriptor specified by index
            and langid from a device.

        Arguments:
            index: index of descriptor in the device.
            length: number of bytes of the string
            langid: Language ID. If it is omittedi, will be
                    used the first language.
        """
        return util.get_string(self.dev, length, index, langid).encode('ascii')

 def serial_number(self):
     return util.get_string(self, 1000, self.iSerialNumber)

 def product(self):
     return util.get_string(self, 1000, self.iProduct)

 def manufacturer(self):
     return util.get_string(self, 1000, self.iManufacturer)

	def __getName(self,pen):
		"""
		Get pen's name for user displaying
		"""
		name = (util.get_string(dev=pen,length=20,index=1))+" "+(util.get_string(dev=pen,length=20,index=2))
		return name

 def get_string(self, num):
     return get_string(self.__dev, num)