Add docstring.
Add docstring.

eibanez/PyMySQL,methane/PyMySQL,jheld/PyMySQL,jwjohns/PyMySQL,mosquito/Tornado-MySQL,yeyinzhu3211/PyMySQL,xjzhou/PyMySQL,lzedl/PyMySQL,anson-tang/PyMySQL,yeyinzhu3211/PyMySQL,boneyao/PyMySQL,pulsar314/Tornado-MySQL,Geoion/Tornado-MySQL,eibanez/PyMySQL,Ting-y/PyMySQL,NunoEdgarGub1/PyMySQL,xjzhou/PyMySQL,lzedl/PyMySQL,nju520/PyMySQL,MartinThoma/PyMySQL,wraziens/PyMySQL,wraziens/PyMySQL,modulexcite/PyMySQL,pymysql/pymysql,PyMySQL/PyMySQL,PyMySQL/Tornado-MySQL,aio-libs/aiomysql,DashaChuk/PyMySQL