如果语句总是打印(Python)

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

这是因为无论你输入什么,至少有一个测试是真的:

>>> 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)

and改为使用:

>>> 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