how to handle value errors in while 1 loop with scheduling it with a Timer class - json

Question

i have written a code to read registers of a modbus communication protocol. i have attached the code below as well.. am able to overcome the i/o errors by exception handling method where as the value error that i get , am not able throw that error and move on.
Basically what i am doing is am reading the data in the registers and sending up to the server. but my requirement is i have to read the values every second and for 24 hours. so i need to build a robust system that will overcome these value errors and continue executing the threads i have created.
the code to read registers is given below :
import minimalmodbus
import serial
from ctypes import *
import struct
import time
minimalmodbus.BAUDRATE = 9600
minimalmodbus.PARITY = serial.PARITY_NONE
minimalmodbus.BYTESIZE = 8
minimalmodbus.TIMEOUT=5
minimalmodbus.CLOSE_PORT_AFTER_EACH_CALL = True
energy_meter = serial.Serial("/dev/ttyUSB0", baudrate=9600,
parity=serial.PARITY_NONE,
stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS, timeout=5)
energy_meter = minimalmodbus.Instrument('/dev/ttyUSB0', 2, mode='rtu')
#energy_meter.debug = True
def convert_in_float(value1, value2):
raw = struct.pack('>HH',value1,value2)
ans = struct.unpack('>f', raw)[0]
return ans
def sdm630():
parameter_list1 = [ 0 ] * 0x12
parameter_list2 = [ 0 ] * 3
parameter_list3 = [ 0 ] * 6
#print energy_meter
error = 0
try:
index = 0
read_values1 = energy_meter.read_registers( 0 , 0x24, 4)
for i in range ( 0, 0x24, 2):
parameter_list1[index] = convert_in_float( read_values1[i], read_values1[i+1])
#print "Parameter read from register : ", hex(index), "is : ", parameter_list1[index] ,"\n"
index = index + 1
#read parameter list 2 & 3 in a similar way
error = 0
return error, parameter_list1, parameter_list2, parameter_list3, int(time.time())
except IOError or ValueError:
print "got error"
error = 1
return error, parameter_list1, parameter_list2, parameter_list3, int(time.time())
also, i have written a separate code to dump all data to server and is shown below :
import time
from pymongo import MongoClient
client = MongoClient('mongodb://10.32.36.40:27017')
db = client.clytics
collection = db['raspberry_pi']
def pushData(error, value1, value2, value3, value4):
if error == 0 :
temp_js = {
#variable assignment
}
temp_js_id = collection.insert(temp_js)
using the above two codes i have created threads for each function. and i only execute this code and after 20 minutes of execution , i get value errors and the program doesnt execute anymore. the main program is given below :
import time
from threading import Thread
from threading import Timer
from Queue import Queue
from modbus import sdm630
from dumpInDB import pushData
from processData import process_the_data
DELAY_SEC = 1
DELAY_MIN = 60
LOOP_LIMIT = 60
def getData(q):
error, parameter_list1, parameter_list2 , parameter_list3, parameter_list4= sdm630()
print "In getData - data:", parameter_list1, parameter_list2
q.put([error, parameter_list1, parameter_list2, parameter_list3, parameter_list4])
def processData(q1,q2):
sec_data = q1.get()
min_data = process_the_data(sec_data)
print "In processData - data:", sec_data, min_data
q2.put(min_data)
print "queue:", q2.qsize()
def putData(q):
#print "In putData - data:", value[0], value[1], value[2]
for i in range(0, q.qsize()):
value = q.get()
print "In putData - data:", value[0], value[1], value[2], value[3]
pushData( value[0], value[1] , value[2], value[3] , value[4])
def thread1(threadName, q):
i = 0
while 1:
t = Timer( DELAY_SEC, getData, args = (q,))
t.start()
time.sleep(DELAY_SEC)
def thread2( threadName, q1,q2):
i = 0
print "in thread2"
while 1:
t = Timer( DELAY_SEC, processData, args = (q1,q2,))
t.start()
time.sleep(DELAY_SEC)
def thread3( threadName, q):
i = 0
print "in thread3"
while 1:
t = Timer( DELAY_MIN, putData, args = (q,))
t.start()
print "schedule time - min"
time.sleep(DELAY_MIN)
queue_second = Queue()
queue_minute = Queue()
thread1 = Thread( target=thread1, args=("Thread-1", queue_second) )
thread2 = Thread( target=thread2, args=("Thread-2", queue_second, queue_minute) )
thread3 = Thread( target=thread3, args=("Thread-3", queue_minute) )
thread1.start()
thread2.start()
thread3.start()
thread1.join()
thread2.join()
thread3.join()
am stuck with this error. shown below :
minimalmodbus.Instrument<id=0xb6b2d9b8, address=2, mode=rtu, close_port_after_each_call=True, precalculate_read_size=True, debug=False, serial=Serial<id=0xb6b482f0, open=False>(port='/dev/ttyUSB0', baudrate=9600, bytesize=8, parity='N', stopbits=1, timeout=5, xonxoff=False, rtscts=False, dsrdtr=False)>
Traceback (most recent call last):
File "topScript.py", line 7, in <module>
from modbus import sdm630
File "/home/pi/scripts/modbus.py", line 60, in <module>
sdm630()
File "/home/pi/scripts/modbus.py", line 32, in sdm630
read_values1 = energy_meter.read_registers( 0 , 0x24, 4)
File "/usr/local/lib/python2.7/dist-packages/minimalmodbus.py", line 498, in read_registers
numberOfRegisters=numberOfRegisters, payloadformat='registers')
File "/usr/local/lib/python2.7/dist-packages/minimalmodbus.py", line 697, in _genericCommand
payloadFromSlave = self._performCommand(functioncode, payloadToSlave)
File "/usr/local/lib/python2.7/dist-packages/minimalmodbus.py", line 798, in _performCommand
payloadFromSlave = _extractPayload(response, self.address, self.mode, functioncode)
File "/usr/local/lib/python2.7/dist-packages/minimalmodbus.py", line 1075, in _extractPayload
raise ValueError(text)
ValueError: Checksum error in rtu mode: '\xa6\xe6' instead of '\xf7[' . The response is: '\xff\xf7HCeN\xce\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00?\x80\x00\x00?\x80\x00\x00?\x80\x00\x00\xa6\xe6' (plain response: '\xff\xf7HCeN\xce\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\
sometimes value error keeps popping up for sometime and finally fails and gives a message saying no more threads can be created.(reached to maximum level)

Answer 1

Your syntax to handle multiple exceptions is wrong. Use something like:
except (ValueError, IOError):
For more details see the Python tutorial https://docs.python.org/2/tutorial/errors.html