Core Python Programming (2nd Edition)

23.1. Web Services
There are many Web services and applications on the Net, providing a wide variety of services. You will
find application programmer interfaces (APIs) from most of the big players today, i.e., Yahoo!, Google,
eBay, and Amazon, to name a few. In the past, APIs have been used just to access data using these
services; however, today's APIs are different. They are rich and fully featured, and you are able to
actually integrate services into your own personal Web sites and Web pages, commonly known as "Mashups."
This is an area of active interest that we will continue to explore (REST, XML, RSS, etc.), but for now,
we are going to take a trip back in time to play around with an older interface that is both useful and
has longevity, the stock quote server from Yahoo! at http://finance.yahoo.com.
23.1.1. Yahoo! Finance Stock Quote Server
If you visit the Web site and pull up a quotation for any stock, you will find a Uniform Resource Locator
(URL) link under the basic quote data labeled "Download Data," which lets users download a CSV file
suitable for importing into Microsoft Excel or Intuit Quicken:
http://finance.yahoo.com/d/quotes.csv?s=GOOG&f=sl1d1t1c1ohgv&e=.csv
If your browser's MIME settings are set correctly, your browser will actually launch Excel with the
resulting data. This is due primarily to the final variable (key-value) pair found in the link, e=.csv. This
variable is actually not used by the server as it always sends back data in CSV format anyway.
If we use our friend urllib.urlopen(), we see that for any stock ticker symbol, one CSV string is
returned:
>>> from urllib import urlopen
>>> u = urlopen('http://quote.yahoo.com/d/
quotes.csv?s=YHOO&f=sl1d1t1c1ohgv')
>>> for row in u:
... print 'row'
...
'"YHOO",30.76,"5/23/
2006","4:00pm",+0.30,31.07,31.63,30.76,28594020\r\n'
>>> f.close()
The string would then have to be manually parsed (by stripping the trailing whitespace and splitting on
the comma delimiter). As an alternative to parsing the data string ourselves, we can use the csv
module, introduced in Python 2.3, which does both the string split and the whitespace strip. Using csv,
we can replace the for loop above with the following assuming all other lines are left intact:
>>> import csv
>>> for row in csv.reader(u):
... print row
...