title: I get an error message when I try FreqDist() in NLTK -- NameError: name 'nltk' is not defined
body: <p>I'm learning about the NLTK and my mac
   is working fine except I have trouble with the FreqDist(). (I saw another question about FreqDist() but he was getting a different error message. TypeError: unhashable type: 'list')
  Here's an example:</p>
  
  <pre><code>&gt;&gt;&gt; from nltk.corpus import brown
  &gt;&gt;&gt; news_text = brown.words(categories='news')
  &gt;&gt;&gt; fdist = nltk.FreqDist([w.lower() for w in news_text])
  
  Traceback (most recent call last):
  
  `  File "&lt;stdin&gt;", line 1, in &lt;module&gt;`
  `NameError: name 'nltk' is not defined`
  </code></pre>
  
  <p>This error message is pretty consistent. I get this message every time I try the FreqDist(). Other commands like - >>> brown.fileids() are fine.</p>
  
  <p>Thanks for your help!</p>