这是我的代码和错误消息:
>>> from nltk.tag.stanford import StanfordTagger
>>> st = StanfordTagger('bidirection-distsim-wsj-0-18.tagger')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/nltk/tag/stanford.py", line 42, in __init__
    verbose=verbose)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/nltk/internals.py", line 597, in find_jar
    raise LookupError('\n\n%s\n%s\n%s' % (div, msg, div))
LookupError: 
===========================================================================
  NLTK was unable to find ! Set the CLASSPATH environment variable.
  For more information, on , see:
    <http://nlp.stanford.edu/software>
===========================================================================
我该如何解决?我真的很想在 Python 中使用 stanford tagger 谢谢!