Found existing installation: six

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):

原因很简单：Scrapy依赖six库，但是系统的six库比较老，安装scrapy需要卸载之后安装一个新的。但是Mac OS本身也依赖six，导致无法删除，因此没有办法安装Scrapy。

解决的方式是：使用virtualenv来安装。

sudo pip install virtualenv
virtualenv scrapyenv
cd scrapyenv
source bin/activate
pip install Scrapy

scrapy startproject yourproject开始你的爬虫之旅