fetchtemp.py

#!/usr/bin/python

"""
 Fetching json data from a networked resource 
 - storing them in a postgres database 

	Data source, e.g. an arduino temperature logger

  Expecting to receive a json string with a "temp"-array listing the
  temperatures from the sensors (it may also contain other information, but
  that will be discarded )
  e.g.
  {"temp":[40.50,20.50,-0.50],
   "address":["2852932640040","28A9D0264006D","2895D76E40050"]}

  The data source is not supposed to have a real time clock. If timestamps are
  needed, they must be set by the database (or added in in this script)

"""

import serial
import time
import logging
import logging.handlers
import ConfigParser
import os
import urllib
import json
import sys

pid=str(os.getpid())
appname="["+pid+"] storedata "
import psycopg2

pid=str(os.getpid())
appname="["+pid+"] storedata "
my_logger = logging.getLogger('MyLogger')
my_logger.setLevel(logging.DEBUG)
handler = logging.handlers.SysLogHandler(address = '/dev/log')
my_logger.addHandler(handler)
my_logger.debug(appname+': Starting up ')

config = ConfigParser.RawConfigParser()
config.read('/etc/homedata/fetchtemp.cfg')

"""
/etc/homedata/fetchtemp.cfg:
[server]
url=http://192.168.0.177/json
[database]
dbhost=localhost
dbusername=username
dbpassword=password
dbdatabase=database 
[system]
waittime=880
shortsleep=5
"""

dbdatabase=config.get('database','dbdatabase')	
dbusername=config.get('database','dbusername')
dbhost=config.get('database','dbhost')
dbpassword=config.get('database','dbpassword')
sleeptime=float(config.get('system','waittime'))
shortsleep=float(config.get('system','shortsleep'))
connstring="dbname='"+dbdatabase+"' user='"+dbusername+"' host='"+dbhost+"' password='"+dbpassword+"'"
#
dbtype='pgsql';

try:
   conn = psycopg2.connect(connstring)
   cur=conn.cursor()
except:
  my_logger.critical(appname+": Unable to connect to the database")
  sys.exit(2)

url=config.get('server','url')
# nosleep=false
sql="select addmeasure(%s,(select id::integer from sensor where sensoraddr=%s))";

while 1:
  nosleep=False 
# When nosleep is true, an error has occured so the data are lost, a new
# attempt to fetch the data will be done shortly (shortsleep secs) after.
  my_logger.debug(appname+": Fetching data from "+url)
  try:
      f = urllib.urlopen(url)
      jsondata=json.load(f)
  except:
      my_logger.error(appname+"Could not fetch data from"+url)
      nosleep=True
  if(nosleep):
      time.sleep(shortsleep)
  else:

      for(i,val) in enumerate(jsondata['temp']):
        try:
           cur.execute(sql,(val,jsondata['address'][i]))
        except:
           my_logger.error(appname+": error 92 :"+str(sys.exc_info()))
      try:
        conn.commit()
      except:
        my_logger.error(appname+": error 96 :"+str(sys.exc_info()))
        nosleep=True
        my_logger.debug(appname+": Finished storing")
      time.sleep(sleeptime)