[py] Fix tornado 4.2 compatibility
[py] Fix tornado 4.2 compatibility

i/tchannel,chenwenbin928/tchannel,hustxiaoc/tchannel,sasa233/tchannel,Zirpon/tchannel,vanloswang/tchannel,hustxiaoc/tchannel,RyanTech/tchannel,vanloswang/tchannel,bunnyblue/tchannel,i/tchannel,RyanTech/tchannel,chenwenbin928/tchannel,bunnyblue/tchannel,i/tchannel,Zirpon/tchannel,sasa233/tchannel,hustxiaoc/tchannel,vanloswang/tchannel,sasa233/tchannel,benfleis/tchannel,savaki/tchannel,bunnyblue/tchannel,savaki/tchannel,savaki/tchannel,RyanTech/tchannel,chenwenbin928/tchannel,Zirpon/tchannel,benfleis/tchannel,benfleis/tchannel