I manage a handful of websites, like this one. Having built a few on other platforms, such as Drupal, I’m familiar with the dreaded error “The website encountered an unexpected error. Please try again later." On sites that I don’t check on frequently, it can be an embarrassment when people begin emailing you with questions about the site being down.

I wrote the following Python script to deal with the problem:

#!/usr/bin/python

import urllib
from subprocess import Popen, PIPE

RECIPIENT = "[email protected]"
URL_TO_CHECK = "http://www.example.com"
ERR_MSG = "Your website is down."

def sendMessage(message):
	scpt = '''
	tell application "Messages" to send "{0}" to buddy "{1}" of (service 1 whose service type is iMessage)
	'''.format(message,RECIPIENT)
	args = []
	p = Popen(['osascript', '-'] + args, stdin=PIPE, stdout=PIPE, stderr=PIPE)
	stdout, stderr = p.communicate(scpt)

try:
	fh = urllib.urlopen(URL_TO_CHECK)
except IOError:
	sendMessage(ERR_MSG)
else:
	# handle database type errors from Drupal sites
	site_content = fh.read()
	target_str = "The website encountered an unexpected error. Please try again later."
	if site_content.find(target_str) != -1:
		sendMessage(ERR_MSG)
	else:
		print "No error"

I run this as a scheduled job using launchd and as long as I have a Messages-capable device with me, I’ll get notifications of issues with the site.

Indigo 6 is a popular home automation controller software package on the Mac. Extensibility is one of its main features and it allows users to add a range of features to suit their needs.

Using Python scripting, users can create plugins that provide extended functionality. These plugins can provide a custom configuration UI to the user. Since the documentation around a particular feature - dynamic lists was lacking, I’ve written up my approach here.

Since I live in Canada, the excellent NOAA plugin doesn’t work for me. However Environment Canada provides an XML-based weather data API that we could package into an Indigo plugin. Since the number of Environment Canada station locations is large, I would like the user to select a province first then select locations within that province. This means that I must use a dynamic list for the locations and reload the location list dynamically when the province changes. The solution turned out to be simple. Perhaps it could be even simpler. This is just what I came up with.

Devices.xml configuration

<?xml version="1.0"?>
<Devices>
    <!-- define devices -->
    <Device type="custom" id="station">
        <Name>Weather station</Name>
        <ConfigUI>
            <!-- choose location -->
            <Field id="province" type="menu">
                <Label>Province:</Label>
                <List class="self" filter="" method="listProvinces"/>
                <CallbackMethod>provinceChanged</CallbackMethod>
            </Field>
            <!-- choose location within province -->
            <Field id="location" type="menu">
                <Label>Location:</Label>
                <List class="self" filter="" method="listStations" dynamicReload="true"/>
            </Field>
        </ConfigUI>
    </Device>
</Devices>

In the device configuration I’ve specified a province field and a location field. The former provides a callback method provinceChanged where I can deal with filtering the locations based on the province selection. The other key here is to make the location field dynamically-reloadable (dynamicReload="true".) By doing this, we get another call to the list generator method listStations when the province is selected.

Province selection callback

In plugin.py, I must provide a callback method provinceChanged to save my selection:

def provinceChanged(self, valuesDict, typeId, devId):
    self.selectedProvince = valuesDict['province']

Here’s where the solution might be simpler. The documentation is ambiguous about the status of valuesDict if the device hasn’t been saved yet. Based on that ambiguity, I decided to save the selected province as an instance variable of my Plugin class.

Providing a filtered location list

My dynamic list generator for the locations takes the selected province instance variable into consideration so that when the list is dynamically reloaded, I get a chance to filter the list by province.

def listStations(self, filter="", valuesDict=None, typeId="", targetId=0):
    locations = []
    stations = []
    self.debugLog(u"Generating stations")
    stations = self.locationDB.stationsForProvice(self.selectedProvince)
    for loc in stations:
        option = loc[0]
        city,province = loc[1].encode('utf-8'),loc[2].encode('utf-8')
        stationName = "{0} ({1})".format(city,province)
        locations.append(stationName)
    return locations

I have a suspicion there’s an easier way. If you know of one, let me know and I’ll share it.