[python] catch specific HTTP error in python

I want to catch a specific http error and not any one of the entire family.. what I was trying to do is --

import urllib2
try:
   urllib2.urlopen("some url")
except urllib2.HTTPError:
   <whatever>

but what I end up is catching any kind of http error, but I want to catch only if the specified webpage doesn't exist!! probably that's HTTP error 404..but I don't know how to specify that catch only error 404 and let the system run the default handler for other events..ny suggestions??

For Python 3.x

import urllib.request
from urllib.error import HTTPError
try:
    urllib.request.urlretrieve(url, fullpath)
except urllib.error.HTTPError as err:
    print(err.code)

Tims answer seems to me as misleading. Especially when urllib2 does not return expected code. For example this Error will be fatal (believe or not - it is not uncommon one when downloading urls):

AttributeError: 'URLError' object has no attribute 'code'

Fast, but maybe not the best solution would be code using nested try/except block:

import urllib2
try:
    urllib2.urlopen("some url")
except urllib2.HTTPError, err:
    try:
        if err.code == 404:
            # Handle the error
        else:
            raise
    except:
        ...

More information to the topic of nested try/except blocks Are nested try/except blocks in python a good programming practice?