相关疑难解决方法(0)

我在下面有一个词典:

colors = {
    "blue" : "5",
    "red" : "6",
    "yellow" : "8",
}

如何索引字典中的第一个条目？

colors[0]将返回一个KeyError明显的原因.

使用NLTK运行Python脚本时我得到了这个:

Traceback (most recent call last):
  File "cpicklesave.py", line 56, in <module>
    pos = nltk.pos_tag(words)
  File "/usr/lib/python2.7/site-packages/nltk/tag/__init__.py", line 110, in pos_tag
    tagger = PerceptronTagger()
  File "/usr/lib/python2.7/site-packages/nltk/tag/perceptron.py", line 140, in __init__
    AP_MODEL_LOC = str(find('taggers/averaged_perceptron_tagger/'+PICKLE))
  File "/usr/lib/python2.7/site-packages/nltk/data.py", line 641, in find
    raise LookupError(resource_not_found)
LookupError:
**********************************************************************
  Resource u'taggers/averaged_perceptron_tagger/averaged_perceptro
  n_tagger.pickle' not found.  Please use the NLTK Downloader to
  obtain the resource:  >>> nltk.download()
  Searched in:
    - '/root/nltk_data'
    - '/usr/share/nltk_data'
    - '/usr/local/share/nltk_data'
    - '/usr/lib/nltk_data'
    - '/usr/local/lib/nltk_data'
**********************************************************************

有谁能解释这个问题？