Import the Libraries

We will start by importing the libraries that we need:

from xml.etree import ElementTree as ET
import urllib
import sys

All three libraries are standard libraries that come with the normal Python distribution.

Create the Class

Next we need to create our class. It will be named 'CurrentInfo' and will contain three functions. In order, they are:

• getCurrents—Does the web access and parsing of the XML data
• output—does the printing to the terminal window.
• DoIt—calls the above functions in the proper order.

Although I stated earlier that most classes have an initialization function, this class won’t have one, because in this case there is really nothing to initialize. We’ll start with our class definition and the first function:

class CurrentInfo:
    def getCurrents(self,debuglevel,Location):

There are three parameters for the getCurrents function. The self parameter won’t take an argument or data. The debuglevel is either a 0 or 1 and is there to be a flag to print debugging information or not. Location is where the Zip code is passed into the function. Next, we check to see if the debug mode is turned on and if so, we print the location Zip code that was passed into the function:

        if debuglevel > 0:
            print "Location = %s" % Location

Connect to the Website

Next we attempt to connect to the WeatherUnderground website to get the XML data. We do this using the try/except error handling set. This is in case we have no Internet connection or the website doesn’t respond in a timely manner. After the try keyword, we set the variable called CurrentConditions to the website URL and include the Zip code at the end:

        try:
            CurrentConditions = _ 'http://api.wunderground.com/auto/wui/geo/WXCurrentObXML/index.xml?query=%s' % Location

Now we set the default timeout for the connection to 8 seconds, and open a socket to the URL we set up using the CurrentConditions variable. If there is no error, we tell the XML parsing routine to grab the XML data from the socket, and then we close the socket:

            urllib.socket.setdefaulttimeout(8)
            usock = urllib.urlopen(CurrentConditions)
            tree = ET.parse(usock)
            usock.close()

If there was an error, then we print an error message to the terminal window, and if the debug mode is set to True, we print the location and use the exit routine from the sys library to terminate the program. The number 1 in the sys.exit(1) line says that there was an error that caused us to terminate early. Usually the code 0 means everything worked well, code 1 means “something weird happened,” and 2 means a command line error occurred.

        except:
            print 'ERROR - Current Conditions - Could not get information from server...'
            if debuglevel > 0:
                print Location
                sys.exit(1)

Now, we are assuming that everything has worked correctly and the parser has gotten the XML data. I’m going to explain the first two parsing commands because all of them are the same except what we are looking for and the variables we assign the data to.

The getCurrents function

The first line (for loc in tree.findall(".//full": ) tells the XML parser to look for the tag named <full>. Every tag with that name is pulled into a list named 'loc'. For each and every item in the list, we assign that item text to the self.location variable. In the case of this data, there are many <full> tags, but they all hold the same data. In the next one, we want to get the observation time. Just in case there is more than one instance, we use a for loop to assign the text to the self.obtime variable. Here is the code for this section:

        # Get Display Location
        for loc in tree.findall(".//full"):
            self.location = loc.text
        # Get Observation time
        for tim in tree.findall(".//observation_time"):
            self.obtime = tim.text
        # Get Current conditions
        for weather in tree.findall(".//weather"):
            self.we = weather.text
        # Get Temp
        for TempF in tree.findall(".//temperature_string"):
            self.tmpB = TempF.text
        #Get Humidity
        for hum in tree.findall(".//relative_humidity"):
            self.relhum = hum.text
        # Get Wind info
        for windstring in tree.findall(".//wind_string"):
            self.winds = windstring.text
        # Get Barometric Pressure
        for pressure in tree.findall(".//pressure_string"):
            self.baroB = pressure.text

That’s the end of the getCurrents function. Now we will work on the output function.

The Output Function

This simply prints the information that we have pulled from the XML file into a “human friendly” format in the terminal window:

    def output(self):
        print 'Weather Information From Wunderground.com'
        print 'Weather info for %s ' % self.location
        print self.obtime
        print 'Current Weather - %s' % self.we
        print 'Current Temp - %s' % self.tmpB
        print 'Barometric Pressure - %s' % self.baroB
        print 'Relative Humidity - %s' % self.relhum
        print 'Winds %s' % self.winds

The DoIt function accepts one parameter, the location Zip code. It then calls the getCurrents function with (in the code below) the debug mode turned off and the location. Then it calls the output function:

    def DoIt(self,Location):
        self.getCurrents(0,Location)
        self.output()

That ends our class. It was very simple, but gives you a good idea how easily a class can be created.

The Main Function

The next bit of code is the main function. Again, it doesn’t do very much for this particular program, but it gives a starting point for our program. The first line will assign the Zip code to the location variable. The second line will create an instance of our class. If it had an __init__ function, that would be called automatically when the class instance is created. Finally we call the DoIt function to start the whole thing off:

def main():
    location = '80013'
    currents = CurrentInfo()
    currents.DoIt(location)

Add the Program Entry Point

The last thing we will do is add the program entry point. We use the two lines starting with if __name__ and ending with main(). There are two built-in variables that Python handles for us. The first is __name__ (that’s two underscore characters, the word ‘name’, and two more underscore characters). The other is just like the one we just described but is __main__ (again two underscores, the word ‘main’, and two more underscores). When you start a Python program from the command line, the __name__ variable is set by Python to __main__, so the interpreter knows that it is supposed to call the main() function. However, because we created a class that does all the work, we can actually treat this as a library and import the CurrentInfo class into another program. In that case, the main() function will not be run, because __name__ will not be __main__ but the name of the program calling it.

#===========================================================
# Main loop
#===========================================================
if __name__ == "__main__":
    main()

The output from our program class is as follows:

Weather Information From Wunderground.com
Weather info for Aurora, Colorado
Last Updated on November 14, 12:55 PM MST
Current Weather - Partly Cloudy
Current Temp - 54 F (12 C)
Barometric Pressure - 29.86 in (1011 mb)
Relative Humidity - 41%
Winds From the SSW at 5 MPH

As an aside, I have tested the source code by changing the location variable data from ‘80013’ to ‘W11 2BQ’. Everything worked as expected.