python-nltk on Ubuntu 12.04 LTS: nltk.download('brown') results in HTML error 401

I have installed python-nltk on Ubuntu Server 12.04 using apt-get.

But when I try to download a corpus, I get the following error:

$ python
Python 2.7.3 (default, Feb 27 2014, 19:58:35)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import nltk
>>> nltk.download('brown')
[nltk_data] Error loading brown: HTTP Error 401: Authorization
[nltk_data]     Required
False

Am I missing some configuration or additional package?

The DEFAULT_URL used in downloader.py of the Ubuntu packaged version still uses:

DEFAULT_URL = 'http://nltk.googlecode.com/svn/trunk/nltk_data/index.xml'

But the current data server is:

DEFAULT_URL = "http://nltk.github.com/nltk_data/"

You can of course install from source or... modify your already installed version to point to the new server like this:

 sudo perl -pi -e 's#DEFAULT_URL = .*#DEFAULT_URL = "http://nltk.github.com/nltk_data/"#' /usr/lib/python2.7/dist-packages/nltk/downloader.py

You can then install the "brown" corpus:

$ python
Python 2.7.6 (default, Mar 22 2014, 22:59:56) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import nltk
>>> nltk.download('brown')
[nltk_data] Downloading package 'brown' to /home/sylvain/nltk_data...
[nltk_data]   Unzipping corpora/brown.zip.
True
>>> from nltk.corpus import brown
>>> brown.words()
['The', 'Fulton', 'County', 'Grand', 'Jury', 'said', ...]
>>> 

It is possible to fix this without changing the source code. Create a custom downloader in python:

>>> dl = nltk.downloader.Downloader("http://nltk.github.com/nltk_data/")

then you open a GUI dialog:

>>> dl.download()

Check you have write access to the download directory and download what you need.