Python script stops running after 15-20h

Question

I'm monitoring my sensor data and sending it online with my .py srcipt. It should run every 5min so I programed it like this:

import threading
import time 

def send_wu():

    # Read sensors
    temperature = sensor.read_temperature()
    humidity,t_old = dht.read_retry(dht.DHT22, 4)
    pressure = (sensor.read_pressure()*0.01)+13 # Correct pressure

    # Prevent wrong reading
    while pressure>1030 or pressure<1000:
        pressure=(sensor.read_pressure()*0.01)+13

    def dewpoint_approximation(T,RH):
        Td = (237.7  * gamma(T,RH)) / (17.271 - gamma(T,RH))
        return Td

    def gamma(T,RH):
        g = (17.271 * T / (237.7  + T)) + log(RH/100.0)
        return g


    dewpoint = dewpoint_approximation(temperature,humidity)


    date = "now"

    data = "http://weatherstation.wunderground.com/weatherstation/updateweatherstation.php?ID=IGRADZAGxx&PASSWORD=xxxxxx&dateutc=now&tempf={0:.1f}&baromin={1}&humidity={2}&dewptf={3}&softwaretype=Custom&action=updateraw".format(temperature*1.8+32,pressure*0.0295299830714,humidity,dewpoint*1.8+32)

    response = urllib2.urlopen(data).read()
    print time.strftime("%Y-%m-%d %H:%M:%S")+" Wunderground: "+response


    # Run every 5 min
    threading.Timer(300, send_wu).start()

It works fine for 15-20h but then it stops, here comes the interesting part. When I fire up the putty it restarts the script and runs it again. What's stoping my script from running?

EDIT:

I managed to "catch" the error:

Exception in thread Thread-317:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 552, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 760, in run
    self.function(*self.args, **self.kwargs)
  File "meteo_stanica.py", line 181, in posalji_wu
    response = urllib2.urlopen(data).read()
  File "/usr/lib/python2.7/urllib2.py", line 127, in urlopen
    return _opener.open(url, data, timeout)
  File "/usr/lib/python2.7/urllib2.py", line 401, in open
    response = self._open(req, data)
  File "/usr/lib/python2.7/urllib2.py", line 419, in _open
    '_open', req)
  File "/usr/lib/python2.7/urllib2.py", line 379, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.7/urllib2.py", line 1211, in http_open
    return self.do_open(httplib.HTTPConnection, req)
  File "/usr/lib/python2.7/urllib2.py", line 1184, in do_open
    r = h.getresponse(buffering=True)
  File "/usr/lib/python2.7/httplib.py", line 1034, in getresponse
    response.begin()
  File "/usr/lib/python2.7/httplib.py", line 407, in begin
    version, status, reason = self._read_status()
  File "/usr/lib/python2.7/httplib.py", line 365, in _read_status
    line = self.fp.readline()
  File "/usr/lib/python2.7/socket.py", line 447, in readline
    data = self._sock.recv(self._rbufsize)
error: [Errno 110] Connection timed out

So the problem is timed out connection, I added "timeout", in 15-20h we'll see if that helps.

response = urllib2.urlopen(data, timeout=20).read()

Answer 1

Network connections will fail once in a while. Best thing to do is handle the failure. The following will handle socket errors. At the top of your file, import socket:

import socket

Then, update your code:

response = urllib2.urlopen(data).read()

with the following:

try:
    response = urllib2.urlopen(data).read()
except socket.error, exc:
    print 'socket error {}, skipping data={}'.format(exc[0], data)

As written above, you'll lose this temperature reading, but the script will keep going. You can make it try to post more than once if you want:

for i in range(3):  # try three times
    try:
        response = urllib2.urlopen(data).read()
    except socket.error, exc:
        print 'socket error {}...'.format(exc[0])
    else:
        break  # success, don't retry
else:
    print 'cannot post, skipping data={}'.format(data)