德摩根定律，
"not (A and B)" is the same as "(not A) or (not B)"also,"not (A or B)" is the same as "(not A) and (not B)".
就您而言，根据第一条陈述，您已经有效地撰写了
if not (i == "" and i == " "):
这是不可能发生的。因此，无论输入是什么，
(i == "" and i == " ")都将始终返回，
False而取反则将
True始终给出。
相反，您应该这样写
if i != "" and i != " ":
或根据De Morgan引用的第二条陈述，
if not (i == "" or i == " "):
