名单有问题

Question

我的代码是：

foods2 = list()
while food2 := input("Which food do you like ? ") != "quit":
    foods2.append(food2)
print(foods2)

我希望输出是来自输入的列表

为什么在输入'quit'之前有三个输入时输出[True, True, True]

Answer 1

您必须使用( )来分离walrus操作符和测试：

foods2 = list()
while (food2 := input("Which food do you like ? ")) != "quit":
    # ^                     -^ - HERE
    foods2.append(food2)
print(foods2)

Answer 2

看看Operator precedence，赋值运算符:=是它们中最低的。这意味着python首先对!=求值，并将其布尔结果赋给food2。可以使用括号更改计算顺序：

foods2 = list()
while (food2 := input("Which food do you like ? ")) != "quit":
    foods2.append(food2)
print(foods2)

Answer 3

作为@tdelaneysaid，这是因为运算符优先级和缺少括号来覆盖它。仅供参考，这里有另一种使用generator function的方法

def ask_user():
    while (ans := input("Which food do you like? ")) != "quit":
        yield ans

foods = [inp for inp in ask_user()]