prepare_lines: Don't modify in-place
prepare_lines: Don't modify in-place

The user of an assertion function would not expect that his input gets
altered (if he wants to reuse the inputted lines).
And it's also not the pythonic way.

tushar-rishav/coala,swatilodha/coala,NalinG/coala,netman92/coala,Balaji2198/coala,andreimacavei/coala,sophiavanvalkenburg/coala,sudheesh001/coala,Shade5/coala,yashtrivedi96/coala,nemaniarjun/coala,CruiseDevice/coala,JohnS-01/coala,RJ722/coala,kartikeys98/coala,Tanmay28/coala,scriptnull/coala,kartikeys98/coala,JohnS-01/coala,swatilodha/coala,vinc456/coala,MattAllmendinger/coala,aptrishu/coala,scriptnull/coala,dagdaggo/coala,SambitAcharya/coala,karansingh1559/coala,Shade5/coala,SambitAcharya/coala,coala/coala,meetmangukiya/coala,rresol/coala,Asnelchristian/coala,SambitAcharya/coala,scriptnull/coala,SanketDG/coala,d6e/coala,coala/coala,damngamerz/coala,refeed/coala,yland/coala,sils1297/coala,rresol/coala,MariosPanag/coala,NalinG/coala,arjunsinghy96/coala,netman92/coala,scriptnull/coala,NalinG/coala,Asalle/coala,tltuan/coala,Nosferatul/coala,damngamerz/coala,sudheesh001/coala,scottbelden/coala,MattAllmendinger/coala,SambitAcharya/coala,d6e/coala,arush0311/coala,mr-karan/coala,AbdealiJK/coala,scriptnull/coala,NiklasMM/coala,NiklasMM/coala,sagark123/coala,shreyans800755/coala,jayvdb/coala,Tanmay28/coala,Tanmay28/coala,nemaniarjun/coala,AdeshAtole/coala,AbdealiJK/coala,Tanmay28/coala,yashLadha/coala,kartikeys98/coala,incorrectusername/coala,saurabhiiit/coala,AdeshAtole/coala,vinc456/coala,meetmangukiya/coala,abhiroyg/coala,sils1297/coala,djkonro/coala,Nosferatul/coala,ManjiriBirajdar/coala,Tanmay28/coala,refeed/coala,swatilodha/coala,MattAllmendinger/coala,impmihai/coala,RJ722/coala,yland/coala,sils1297/coala,impmihai/coala,rimacone/testing2,arush0311/coala,ManjiriBirajdar/coala,aptrishu/coala,Shade5/coala,CruiseDevice/coala,rimacone/testing2,karansingh1559/coala,karansingh1559/coala,tushar-rishav/coala,andreimacavei/coala,dagdaggo/coala,tltuan/coala,andreimacavei/coala,Uran198/coala,coala-analyzer/coala,SambitAcharya/coala,stevemontana1980/coala,incorrectusername/coala,lonewolf07/coala,coala/coala,lonewolf07/coala,arafsheikh/coala,refeed/coala,d6e/coala,MariosPanag/coala,jayvdb/coala,ayushin78/coala,sagark123/coala,yashLadha/coala,coala-analyzer/coala,dagdaggo/coala,Uran198/coala,yland/coala,AbdealiJK/coala,shreyans800755/coala,aptrishu/coala,stevemontana1980/coala,RJ722/coala,jayvdb/coala,SambitAcharya/coala,svsn2117/coala,mr-karan/coala,abhiroyg/coala,tltuan/coala,yashtrivedi96/coala,mr-karan/coala,SanketDG/coala,ManjiriBirajdar/coala,arjunsinghy96/coala,JohnS-01/coala,svsn2117/coala,shreyans800755/coala,coala-analyzer/coala,stevemontana1980/coala,scottbelden/coala,rresol/coala,meetmangukiya/coala,ayushin78/coala,abhiroyg/coala,damngamerz/coala,Uran198/coala,MariosPanag/coala,NalinG/coala,SanketDG/coala,NalinG/coala,vinc456/coala,Asnelchristian/coala,yashtrivedi96/coala,AdeshAtole/coala,sagark123/coala,sudheesh001/coala,Nosferatul/coala,scottbelden/coala,CruiseDevice/coala,nemaniarjun/coala,sophiavanvalkenburg/coala,Tanmay28/coala,djkonro/coala,sophiavanvalkenburg/coala,rimacone/testing2,djkonro/coala,Tanmay28/coala,SambitAcharya/coala,lonewolf07/coala,scriptnull/coala,saurabhiiit/coala,svsn2117/coala,arush0311/coala,arjunsinghy96/coala,Tanmay28/coala,arafsheikh/coala,scriptnull/coala,saurabhiiit/coala,tushar-rishav/coala,NalinG/coala,netman92/coala,impmihai/coala,Balaji2198/coala,yashLadha/coala,NalinG/coala,Asnelchristian/coala,arafsheikh/coala,ayushin78/coala,NiklasMM/coala,incorrectusername/coala,Asalle/coala,Asalle/coala,Balaji2198/coala