Question

我正在尝试添加if语句来检查无效输入。如果用户输入“是”并且如果用户输入“否”则结束，它就像它应该的那样工作并再循环回来。但是出于某些奇怪的原因，无论答案是什么：是，否，随机字符等。它总是打印“无效输入”语句。当答案不是“是”或“否”时，我试图将其打印出来。

while cont == "Yes":
    word=input("Please enter the word you would like to scan for. ") #Asks for word
    capitalized= word.capitalize()  
    lowercase= word.lower()
    accumulator = 0

    print ("\n")
    print ("\n")        #making it pretty
    print ("Searching...")

    fileScan= open(fileName, 'r')  #Opens file

    for line in fileScan.read().split():   #reads a line of the file and stores
        line=line.rstrip("\n")
        if line == capitalized or line == lowercase:
            accumulator += 1
    fileScan.close

    print ("The word", word, "is in the file", accumulator, "times.")

    cont = input ('Type "Yes" to check for another word or \
"No" to quit. ')  #deciding next step
    cont = cont.capitalize()

    if cont != "No" or cont != "Yes":
        print ("Invalid input!")

print ("Thanks for using How Many!")  #ending

Answer 1

那是因为无论你输入什么，至少一个的测试是真的：

>>> cont = 'No'
>>> cont != "No" or cont != "Yes"
True
>>> (cont != "No", cont != "Yes")
(False, True)
>>> cont = 'Yes'
>>> cont != "No" or cont != "Yes"
True
>>> (cont != "No", cont != "Yes")
(True, False)

改为使用and：

>>> cont != 'No' and cont != 'Yes'
False
>>> cont = 'Foo'
>>> cont != 'No' and cont != 'Yes'
True

或使用会员资格测试（in）：

>>> cont not in {'Yes', 'No'}  # test against a set of possible values
True

Answer 2

if cont != "No" or cont != "Yes":

Yes和No都满足这个条件

应为cont != "No" and cont != "Yes"

Answer 3

Cont将始终不等于“否”或不等于“是”。您需要and而不是or。

或者，或者，

if cont not in ['No', 'Yes']:

如果你想要更加可扩展，例如，添加小写。

Answer 4

if cont != "No" or cont != "Yes"表示“如果答案不是否，则表示不是”。一切都不是否是，是的，因为它不能同时存在。

将其改为if cont not in ("Yes", "No")。

Answer 5

您需要and操作而不是or。使用或操作，无论输入值是什么，您的条件都将评估为真。将条件更改为：

if cont != "No" and cont != "Yes":

或只是使用：

if cont not in ("No", "Yes"):

Answer 6

if cont != "No" or cont != "Yes":

你可能输入什么不能满足这个要求？

如果语句总是打印（Python）

6 个答案: