Python's `urllib2`: Why do I get error 403 when I `urlopen` a Wikipedia page?

Question

I have a strange bug when trying to urlopen a certain page from Wikipedia. This is the page:

http://en.wikipedia.org/wiki/OpenCola_(drink)

This

Answer 1

Wikipedias stance is:

Data retrieval: Bots may not be used to retrieve bulk content for any use not directly related to an approved bot task. This includes dynamically loading pages from another website, which may result in the website being blacklisted and permanently denied access. If you would like to download bulk content or mirror a project, please do so by downloading or hosting your own copy of our database.

That is why Python is blocked. You're supposed to download data dumps.

Anyways, you can read pages like this in Python 2:

req = urllib2.Request(url, headers={'User-Agent' : "Magic Browser"}) 
con = urllib2.urlopen( req )
print con.read()

Or in Python 3:

import urllib
req = urllib.request.Request(url, headers={'User-Agent' : "Magic Browser"}) 
con = urllib.request.urlopen( req )
print(con.read())