最近开始研究自然语言处理了，所以准备好好学习一下，就跟着《Python自然语言处理》这本书，边学边整理吧
安装
Mac里面自带了python2.7，所以直接安装nltk就可以了。
默认执行sudo pip install -U nltk会报错：
Collecting nltk
Downloading nltk-3.2.4.tar.gz (1.2MB)
100% |████████████████████████████████| 1.2MB 555kB/s
Collecting six (from nltk)
Downloading six-1.11.0-py2.py3-none-any.whl
Installing collected packages: six, nltk
Found existing installation: six 1.4.1
DEPRECATION: Uninstalling a distutils installed project (six) has been deprecated and will be removed in a future version. This is due to the fact that uninstalling a distutils project will only partially uninstall the project.
Uninstalling six-1.4.1:
这是因为系统内部已经有six包了，不能被修改。所以可以跳过six，直接安装nltk
sudo pip install -U nltk --ignore-installed six
这样可以看到输出：
Collecting nltk
Downloading nltk-3.2.4.tar.gz (1.2MB)
100% |████████████████████████████████| 1.2MB 552kB/s
Collecting six
Downloading six-1.11.0-py2.py3-none-any.whl
Installing collected packages: six, nltk
Running setup.py install for nltk ... done
测试一下：
xingoodeMacBook-Pro:~ xingoo$ python
Python 2.7.10 (default, Feb 7 2017, 00:08:15)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.34)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import nltk
没有错误，说明安装成功了。
下载数据集
然后就可以下载数据集了，执行命令nltk.download()弹出下载对话框。点击下载就可以用nltk为我们提供的语料库了。
参考
《python自然语言处理》