def cat( *args,sep="/" ):
    print(sep.join(args))

concat("111","aaa","222")
concat("111","aaa","222",sep=".")

python2中執(zhí)行

: def cat( *args,sep="/" ):
SyntaxError: invalid syntax
    
python3中執(zhí)行  

111/aaa/222
111.aaa.222