在mac上安装nltk
nltk官网教程：http://www.nltk.org/install.html
第一步是 Install NLTK: run sudo pip install -U nltk
但是出现问题，没有 pip 命令
然后找到这个教程：http://blog.csdn.net/lqzitongyezu/article/details/47664947
按照上面这个教程，成功安装pip。
但是走到最后的第4步和第5步，又出现如下问题：
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:
Exception:
Traceback (most recent call last):
...............省略
最后找到这个博客：https://www.cnblogs.com/chxw2017/p/6837100.html
需要在sudo pip install -U nltk命令后面加上--upgrade --ignore-installed six
xxxdeMacBook-Pro:~ xxx$ sudo pip install -U nltk --upgrade --ignore-installed six
The directory '/Users/zhouziyun/Library/Caches/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/Users/zhouziyun/Library/Caches/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
Collecting nltk
Downloading nltk-3.2.5.tar.gz (1.2MB)
100% |████████████████████████████████| 1.2MB 123kB/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
Successfully installed nltk-3.2.5 six-1.11.0
xxxMacBook-Pro:~ xxx$ python
Python 2.7.10 (default, Jul 15 2017, 17:16:57)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import nltk
>>>