对python中的While循环感到困惑

Question

while循环真的让我很困惑。它说while循环将在条件为True时执行。那么，根据下面的算法，只有当我们没有输入"quit"时，消息才会被打印出来，对吗?然而，当我输入'quit'时，quit仍然在结束循环之前被打印出来。

为什么?有关于while循环的介绍吗?谢谢!

prompt = "Please let me know what toppings you prefer?"
prompt += "Enter 'quit' to end the order. "
message = ""
while message != 'quit':
message = input (prompt)
print (message)

Answer 1

是的，这是假定的行为，因为检查while条件只会在每次循环完成时发生。

while message != 'quit':    #3. Loop again for condition checking here
message = input (prompt)  #1. Your input is 'quit' here
print (message)           #2. 'quit' gets printed

#4. found that the condition is false and finally breaks the loop

所以对于你的情况，我猜是你不想在控制台上输入'quit'后打印'quit'消息，你可以这样做:

while True:
message = input (prompt)
if message == 'quit':
break
else:
print(message)

使用一个永远连续的循环，但在其内部进行条件检查，并在条件满足时使用break关键字。

Answer 2

你可以试试这个

# This code creates an empty list called "prompts" and then appends two strings
# to it, representing prompts for the user. 
prompts =[]
prompts.append("Please let me know what toppings you prefer?")
prompts.append("Enter 'quit' to end the order. ")
# An empty list called "responses" is created to store the user's input
responses = []
# The code enters a while loop which will continue until the string 'quit' 
# is entered by the user
while 'quit' not in responses:
# for each prompt in the prompts list, the code will ask the user for input
# and append the input to the responses list
for prompt in prompts:
responses.append(input(prompt))

Answer 3

第一次执行while循环时，message变量不等于"quit"，因此内部部分将执行

你可能想这样做:

prompt = "Please let me know what toppings you prefer?Enter 'quit' to end the order. "
while message:=input(prompt) != "quit": print(message)

使用python 3.8版本

中的walrus操作符