Notes:
Lesson 3.7: Accessing the web – providing a weather forecast
from urllib.request import urlopen from xml.dom import minidom import time
# extract weather details by grabbing tags from the RSS feed # 'channel' contains all titles that contain weather heading text def ExtractWeather (doc): for node in doc.getElementsByTagName( 'channel' ): for title in node.getElementsByTagName( 'title' ): print (title.firstChild.data) results = [] bbc_weather = "http://open.live.bbc.co.uk/weather/feeds/en/" locations = [ "2653941" , "2655603" , "2633352" , "2653822" , "2650752" ] forecast = "/3dayforecast.rss" start = time.time() for location in locations: # open the rss feed and parse the result into a web document # and add the doc to the end of the list results.append(minidom.parse(urlopen(bbc_weather+location+ forecast))) elapsedTime = (time.time() - start)) for webDoc in results: ExtractWeather(webDoc) print ( "Elapsed Time: %s" % elapsedTime)
We’re getting to the end of the experiments now, and these will require you to have a web connection. The first part of this experiment shows you how to get weather reports from an RSS feed . An RSS feed is like a trimmed-down webpage with only a standard set of data that can be grabbed and displayed. Whenever you look at a webpage or an RSS feed, you are really grabbing a list of instructions on how to draw the page in your web browser or feed reader. This program is set up to find the three-day forecast for five different locations in the UK. It grabs the pages into what is known as a “ Document ” and then it extracts the information marked as “titles” from that document. These contain the forecast data on the RSS feed. The main function for grabbing web data is “urlopen”. A URL is a “ uniform resource locator ”, which is the internet equivalent of a street address for anything and everything on the web. A call to “urlopen” will stop the Python program until it finds what you are looking for and returns a result. This might take less than a second but it could also take several seconds. This might be a problem, and it explains why you have to wait for your browser to respond to some webpages. This program may take a few seconds before it completes fetching all five reports. The listing takes a snapshot of the time before calling “urlopen” and again after it completes so that it can show you how long it took.
Experiments in Python
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