python dowload

[monkeys paw]

I used the following code to download a PDF file, but the
file was invalid after running the code, is there problem
with the write operation?

import urllib2
url = 'http://www.whirlpoolwaterheaters.com/downloads/6510413.pdf'
a = open('adobe.pdf', 'w')
for line in urllib2.urlopen(url):
     a.write(line)