Handling Multiple USB ports in Python

[samalpramod]

Hi,
I am new to python and to the forum too. In my python application I have to read from two USB ports and process the data I get from any of the USB port. For one port I am using pyUSB to read data from the device. On another USB port is attached a device for which I am using method from shared object library(.so file). If I rung the functions independently I get the desired response from each USB port. But If I run the application in a while loop alternately I can only get the response from port that I am reading using pyUsb.
Here is my sample code. Please let me know if the approach is incorrect or I have to follow some other approach.

import usb.core import array import usb.util from time import sleep import ctypes devStatus = False ep = None interfaceNo = None eaddr = None dev = None def hid2ascii(lst):	assert len(lst) == 8, 'Invalid data length (needs 8 bytes)'	conv_table = { 0:['', ''], 4:['a', 'A'], 5:['b', 'B'], 6:['c', 'C'], 7:['d', 'D'], 8:['e', 'E'], 9:['f', 'F'], 10:['g', 'G'], 11:['h', 'H'], 12:['i', 'I'], 13:['j', 'J'], 14:['k', 'K'], 15:['l', 'L'], 16:['m', 'M'], 17:['n', 'N'], 18:['o', 'O'], 19:['p', 'P'], 20:['q', 'Q'], 21:['r', 'R'], 22:['s', 'S'], 23:['t', 'T'], 24:['u', 'U'], 25:['v', 'V'], 26:['w', 'W'], 27:['x', 'X'], 28:['y', 'Y'], 29:['z', 'Z'], 30:['1', '!'], 31:['2', '@'], 32:['3', '#'], 33:['4', '$'], 34:['5', '%'], 35:['6', '^'], 36:['7' ,'&'], 37:['8', '*'], 38:['9', '('], 39:['0', ')'], 40:['\n', '\n'], 41:['\x1b', '\x1b'], 42:['\b', '\b'], 43:['\t', '\t'], 44:[' ', ' '], 45:['_', '_'], 46:['=', '+'], 47:['[', '{'], 48:[']', '}'], 49:['\\', '|'], 50:['#', '~'], 51:[';', ':'], 52:["'", '"'], 53:['`', '~'], 54:[',', '<'], 55:['.', '>'], 56:['/', '?'], 100:['\\', '|'], 103:['=', '='], }	# A 2 in first byte seems to indicate to shift the key. For example # a code for ';' but with 2 in first byte really means ':'.	if lst[0] == 2:	shift = 1	else:	shift = 0	# The character to convert is in the third byte	ch = lst[2]	if ch not in conv_table:	print "Warning: data not in conversion table"	return ''	return conv_table[ch][shift] def getQRDevice():	global devStatus	global ep	global interfaceNo	global eaddr	global dev	dev = usb.core.find(idVendor=0x2dd6, idProduct=0x26c1)	if (dev):	ep = dev[0].interfaces()[0].endpoints()[0]	interfaceNo = dev[0].interfaces()[0].bInterfaceNumber	dev.reset()	if dev.is_kernel_driver_active(interfaceNo):	dev.detach_kernel_driver(interfaceNo)	dev.set_configuration()	eaddr = ep.bEndpointAddress	print('Device connected')	devStatus = True;	else:	print('Device not connected')	return False; def getQR():	if (devStatus == True):	data = None	line = ''	while data is None:	try:	readData = dev.read(eaddr,1024)	#print(readData)	ch = hid2ascii(readData)	line += ch	if len(line)>0 and ch =='\n':	print(line)	return line;	break	except usb.core.USBError as e:	data = None	if e.args == ('Operation timed out'):	continue def detect(): obj = ctypes.CDLL('/home/pramod/testpython/for_so/dualcard_main.so') o = obj.DualiUSBOpen() while(o): s=" "	s=s.rjust(128," ")	c = obj.DualiUSBFind(0,s)	print("c : " + str(c))	if c>=0: s="" s=s.rjust(128," ") card = obj.DualiUSBFind(0,s) print("card obj"+str(card)) print("scard="+s) if card>=0: #submit_to_tkinter(label2,"Remove Card/QR") detected = "card" card = None break else: s="" s = getQR() print("sqr="+s) if len(s)>0: #submit_to_tkinter(label2,"Remove Card/QR") detected = "qr" break return s,detected if __name__=='__main__': #check Card reader	devNFC = usb.core.find(idVendor=0x1db2, idProduct=0x0650)	getQRDevice()	if (devNFC is not None and devStatus==True):	while(1):	dump3 = detect()	s = dump3[0]	detected = dump3[1]	print("s")	print(s)	print("detected : "+detected)	sleep(1)	else:	raise ValueError('Device not found')

Thanks
Pramod