程序忽略if和elif语句

Question

我现在很困惑，完全不知道为什么这个代码不管用。它只执行了else语句，其他的都被忽略了。我不知道是什么原因，求助！

这个程序实在是太简单了，根本不应该出错，可是现在就是不工作。

def main(): #the main function, where the program is held.
    print("Opening Account List now...\n")#flavor tx to add user context for the list of numbers to be displayed.

    infile = open('CHarge Accounts.txt', 'r')#opens the 'CHarge Accounts' text file in read-only mode,
                                            #and saves it to the variable 'infile'.
    numbers = infile.readlines()#The '.readlines()' command opens the text file stored in the 'infile'
                                #variable and and reads every single line of text in the file.
                                #It then saves the data that has been read to the variable 'numbers'.

    infile.close()#This closes the text file being within the 'infile' variable, preventing data from being los,
                  #and causing errors in the program

    index = 0#control value for the number of values to be inserted into the 'numbers' list.
             # 

    while index < len(numbers): #while the index value is less than the number of values within numbers.
                                #This means that as long as index is less than however many account numbers
                                #that are within the 'numbers' list, the loop will continue.

        numbers[index] = int(numbers[index])#While the loop runs, the values in the numbers index will be
                                            #converted to integer values 
        index += 1 #controlling value increments for every number read

    print (numbers, '\n')
    x = 0 #control value for the while loop.
    while x == 0: #Loop begins.
        accnumber = int(input("Please type in the account number you'd like to change, or type in -1 to exit."))

        if accnumber not in numbers and not -1:#Checks if account number is not in the saved txt file data, and
                                               #if the user has inputted the 'kill' value.

            print("The account number you have typed in is invalid.")#informs user data is invalid
        elif accnumber in numbers and not -1:#Checks if the account number is within the saved text file data, and
                                             #if the user has inputted the 'kill' value.

            print("The account number you have selected is valid.")#text informs user that data is valid
        elif accnumber == -1:#Checks if the account number value is -1
            print("Goodbye!")#Flavor for the user
            x = 1 #activates the control variable to break the loop
main()

Answer 1

你的代码有点乱。在添加注释的时候，请尽量让它更容易让人理解。另外，多花点时间在基础语法上！

def main():
    print("Opening Account List now...\n")

    infile = open('CHarge Accounts.txt', 'r')
    numbers = infile.readlines()

    infile.close()

    index = 0
    while index < len(numbers): 
        numbers[index] = int(numbers[index])

        index += 1

    print (numbers, '\n')
    x = 0 #control value for the while loop.
    while x == 0: 
        accnumber = int(input("Please type in the account number you'd like to change, or type in -1 to exit."))

        if (accnumber not in numbers) and (accnumber !=-1):
            print("The account number you have typed in is invalid.")

        elif (accnumber in numbers) and (accnumber !=-1):
            print("The account number you have selected is valid.")#text informs user that data is valid

        elif accnumber == -1:#Checks if the account number value is -1
            print("Goodbye!")#Flavor for the user
            x = 1 #activates the control variable to break the loop

main()

Answer 2

if accnumber not in numbers and not -1:
                              # ^^^^^^ 

在判断真假时，数字0被认为是False，而其他任何整数都被认为是True。所以-1就是True，而not -1就是False，并且(任何东西) and not -1总是False。

因此，你的if和elif语句总是被跳过。

试试

if accnumber not in numbers and accnumber != -1:

这个。

另外：

• 你的注释写得太多，反而让程序看起来很乱。我猜这可能是某种课程要求，也就是说要注释每一行？

• 你使用while循环和索引变量的方式很不常见，可以用列表推导式来替代，像这样：

.

def main():
    print("Opening Account List now...\n")

    with open('Charge Accounts.txt') as inf:
        numbers = [int(line) for line in inf]
    print(numbers, '\n')

    while True:
        accnumber = int(input("Please enter an account number (or -1 to exit): "))
        if accnumber == -1:
            print("Goodbye!")
            break
        elif accnumber not in numbers:
            print("The account number you have typed in is invalid.")
        else:
            print("The account number you have selected is valid.")

main()