First download and ensure that your stopwords
are already downloaded, see http://www.nltk.org/data:
>>> import nltk
>>> packages = ['stopwords']
>>> downloader.download(packages)
>>>
>>> stop = stopwords.words('english')
>>> sent = 'this is a foobar sentence'.split()
>>> [word for word in sent if word not in stop]
['foobar', 'sentence']