six是用来兼容python 2 和 3的，我猜名字就是用的2和3的最小公倍数。
six.moves 是用来处理那些在2 和 3里面函数的位置有变化的，直接用six.moves就可以屏蔽掉这些变化
Python 3 reorganized the standard library and moved several functions to different modules. Six provides a consistent interface to them through the fake six.moves module. For example, to load the module for parsing html on Python 2 or 3, write:
from six.moves import html_parser
Similarly, to get the function to reload modules, which was moved from the builtin module to the imp module, use:
from six.moves import reload_module