s=”Hello”, t=”world”, s+=t, 则 s*3、s[-1]、s[2:8]、 s[::3]、 s[-2::-1]的源代码

s="Hello", t="world", s=t
s*3 # 输出："worldworldworld"
s[-1] # 输出："d"
s[2:8] # 输出："rldwor"
s[::3] # 输出："wol"
s[-2::-1] # 输出："dlrow"