Fix signature on Python 3.x
Fix signature on Python 3.x

aleksandr-bakanov/astropy,tbabej/astropy,funbaker/astropy,dhomeier/astropy,AustereCuriosity/astropy,stargaser/astropy,dhomeier/astropy,AustereCuriosity/astropy,dhomeier/astropy,AustereCuriosity/astropy,mhvk/astropy,bsipocz/astropy,DougBurke/astropy,pllim/astropy,saimn/astropy,astropy/astropy,larrybradley/astropy,astropy/astropy,DougBurke/astropy,DougBurke/astropy,stargaser/astropy,lpsinger/astropy,StuartLittlefair/astropy,larrybradley/astropy,MSeifert04/astropy,MSeifert04/astropy,astropy/astropy,stargaser/astropy,mhvk/astropy,joergdietrich/astropy,StuartLittlefair/astropy,larrybradley/astropy,StuartLittlefair/astropy,astropy/astropy,mhvk/astropy,saimn/astropy,joergdietrich/astropy,AustereCuriosity/astropy,lpsinger/astropy,stargaser/astropy,lpsinger/astropy,dhomeier/astropy,bsipocz/astropy,StuartLittlefair/astropy,tbabej/astropy,pllim/astropy,joergdietrich/astropy,larrybradley/astropy,pllim/astropy,tbabej/astropy,kelle/astropy,tbabej/astropy,AustereCuriosity/astropy,aleksandr-bakanov/astropy,MSeifert04/astropy,StuartLittlefair/astropy,saimn/astropy,pllim/astropy,kelle/astropy,aleksandr-bakanov/astropy,kelle/astropy,kelle/astropy,MSeifert04/astropy,funbaker/astropy,DougBurke/astropy,astropy/astropy,bsipocz/astropy,funbaker/astropy,funbaker/astropy,tbabej/astropy,pllim/astropy,saimn/astropy,larrybradley/astropy,saimn/astropy,bsipocz/astropy,lpsinger/astropy,joergdietrich/astropy,dhomeier/astropy,mhvk/astropy,mhvk/astropy,joergdietrich/astropy,lpsinger/astropy,aleksandr-bakanov/astropy,kelle/astropy