NLTK and language detection

How do I detect what language a text is written in using NLTK?

The examples I've seen use nltk.detect, but when I've installed it on my mac, I cannot find this package.

Have you come across the following code snippet?

english_vocab = set(w.lower() for w in nltk.corpus.words.words())
text_vocab = set(w.lower() for w in text if w.lower().isalpha())
unusual = text_vocab.difference(english_vocab) 

from http://groups.google.com/group/nltk-users/browse_thread/thread/a5f52af2cbc4cfeb?pli=1&safe=active

Or the following demo file?

https://web.archive.org/web/20120202055535/http://code.google.com/p/nltk/source/browse/trunk/nltk_contrib/nltk_contrib/misc/langid.py

This library is not from NLTK either but certainly helps.

$ sudo pip install langdetect

Supported Python versions 2.6, 2.7, 3.x.

>>> from langdetect import detect

>>> detect("War doesn't show who's right, just who's left.")
'en'
>>> detect("Ein, zwei, drei, vier")
'de'

https://pypi.python.org/pypi/langdetect?

P.S.: Don't expect this to work correctly always:

>>> detect("today is a good day")
'so'
>>> detect("today is a good day.")
'so'
>>> detect("la vita e bella!")
'it'
>>> detect("khoobi? khoshi?")
'so'
>>> detect("wow")
'pl'
>>> detect("what a day")
'en'
>>> detect("yay!")
'so'

Although this is not in the NLTK, I have had great results with another Python-based library :

https://github.com/saffsd/langid.py

This is very simple to import and includes a large number of languages in its model.