Python script to read a USB scale in the Linux

readscale.py

#!/usr/bin/python
import os, time
import usb.core
import usb.util
import pygtk
pygtk.require('2.0')
import gtk
from sys import exit
import math

# DYMO M25
VENDOR_ID = 0x0922
PRODUCT_ID = 0x8004

# USPS 75lb scale (doesn't work yet...)
#VENDOR_ID = 0x04d9
#PRODUCT_ID = 0x8010

# find the USB device
dev = usb.core.find(idVendor=VENDOR_ID,
                       idProduct=PRODUCT_ID)

def main():
    try:
        # was it found?
        if dev is None:
            print "device not found"
            exit()
        else:
            devmanufacturer = usb.util.get_string(dev, 256, 1)
            devname = usb.util.get_string(dev, 256, 2)
            print "device found: " + devmanufacturer + " " + devname

            interface = 0
            if dev.is_kernel_driver_active(interface) is True:
                print "but we need to detach kernel driver"
                dev.detach_kernel_driver(interface)

                # use the first/default configuration
                dev.set_configuration()
                print "claiming device"
                usb.util.claim_interface(dev, interface)

                # XXX would be good to release it when we're done:
                # 
                # print "release claimed interface"
                # usb.util.release_interface(dev, interface)
                # print "now attaching the kernel driver again"
                # dev.attach_kernel_driver(interface)
                # print "all done"

            listen()

    except KeyboardInterrupt as e: 
        print "\nquitting"
        exit();


def grab():
    try:
        # first endpoint
        endpoint = dev[0][(0,0)][0]

        # read a data packet
        attempts = 10
        data = None
        while data is None and attempts > 0:
            try:
                data = dev.read(endpoint.bEndpointAddress,
                                   endpoint.wMaxPacketSize)
            except usb.core.USBError as e:
                data = None
                if e.args == ('Operation timed out',):
                    attempts -= 1
                    print "timed out... trying again"
                    continue

        return data
    except usb.core.USBError as e:
        print "USBError: " + str(e.args)
    except IndexError as e:
        print "IndexError: " + str(e.args)


def listen():
    DATA_MODE_GRAMS = 2
    DATA_MODE_OUNCES = 11

    last_raw_weight = 0
    last_raw_weight_stable = 4

    print "listening for weight..."

    while True:
        time.sleep(.5)

        weight = 0
        print_weight = ""

        data = grab()
        if data != None:
            raw_weight = data[4] + data[5] * 256

        # +/- 2g
        if raw_weight > 0 and abs(raw_weight-last_raw_weight) > 0 and raw_weight != last_raw_weight:
            last_raw_weight_stable = 4
            last_raw_weight = raw_weight

        if raw_weight > 0 and last_raw_weight_stable >= 0:
            last_raw_weight_stable -= 1

        if raw_weight > 0 and last_raw_weight_stable == 0:
            if data[2] == DATA_MODE_OUNCES:
                ounces = raw_weight * 0.1
                weight = math.ceil(ounces)
                print_weight = "%s oz" % ounces
            elif data[2] == DATA_MODE_GRAMS:
                grams = raw_weight
                weight = math.ceil(grams)
                print_weight = "%s g" % grams

            print "stable weight: " + print_weight

            clipboard = gtk.clipboard_get()
            clipboard.set_text(str(weight))
            clipboard.store()


def probe():
    for cfg in dev:
        print "cfg: " + str(cfg.bConfigurationValue)
        print "descriptor: " + str(usb.util.find_descriptor(cfg, find_all=True, bInterfaceNumber=1))
        for intf in cfg:
            print "interfacenumber, alternatesetting: " + str(intf.bInterfaceNumber) + ',' + str(intf.bAlternateSetting)
            for ep in intf:
                print "endpointaddress: " + str(ep.bEndpointAddress)


#probe()
main()

Is there a way to check if the scanner has been turned off?

Ideally, I would want the script to continue working if the scale is turned off, then turned back on.

Edit - I have also forked this script and added functionality to notify of zero weight.

I am facing a problem:
The code is always throwing an exception after you try to exectue
data = dev.read(endpoint.bEndpointAddress,
endpoint.wMaxPacketSize)

[Errno 75] Overflow

You have any idea how to fix this ?

I have the same issue: [Errno 75] Overflow

Any ideas?

This script should work with "LIDL Sanitas SBF 48 USB", this device has same USB ID 04d9:8010

Does anyone have any idea how to disable the 3 minute auto turn off so the script can run for longer? I'm trying to track weight change over time and if the weight doesn't change for three minutes the scales turn off and theres no way to bring them back on without physically pressing the button.

Any luck with the errors that @orangeman and @unclesamer pointed out?

usb.core.USBError: [Errno 75] Overflow

@oswinrodrigues actually i am still facing the same issue, did you manage to find a solution ?