循环使用if状态的python程序

Question

我正在编写一个python程序，它将加密和解密一个文件。我的代码中的所有公式都应该工作得很好，但是我的实际循环有问题。我希望向用户提供加密、解密或退出的选项。一旦他们作出选择，并通过这个过程，我希望程序自动再次问他们同样的问题，直到他们选择退出程序。

我很感激任何关于我能解决或可能做错的事情的建议。

编辑:为了澄清，我现在的代码将继续只循环用户最初选择的内容。在它们退出之前，它不允许它们连续选择、加密或解密。

下面是负责循环的主要功能：

def main():
    print("Welcome to the Vigenere-cipher Encryption/Decryption Program\n")
    validStrings = ['e', 'd', 'x']
    userInput = input("Would you like to (e)ncrypt a file, (d)ecrypt a file, or e(x)it (enter e, d, or x)? ")
    while userInput not in validStrings:
        userInput = input("Sorry, that's an invalid choice. Please enter only e, d, or x: ")

    if userInput == 'e':
        while True:
            path = input("Enter the text-file name to encrypt: ")
            if osp.exists(path):
                encrypt(path)
            else:
                print("Sorry the file", path, "does NOT exist -- please try again!") 

    elif userInput == 'd':
        path = input("Enter the text-file name to decrypt: ")
        if osp.exists(path):
            fileName,fileExtension = osp.split(path)
            fileName = fileName+".txt"
            if osp.exists(fileName):
                print("WARNING: The file '%s' already exists!" %fileName)

                ch = input("Is it okay to wipe it out (y/n)? ")
                if ch == 'n':
                    fileName = input("Enter the file name text that should be used (.txt extension will automatically be added) ")
                    fileName = fileName + ".txt"
                elif ch == 'y':
                    pass
            decrypt(path, fileName)

    elif userInput == 'x':
        print("Program Complete!")
        return

Answer 1

如果在程序中选择(e)ncrypt中的选项，则进入一个退出条件始终为真的while循环。在这个循环中，即使您输入了一个有效的文件名，循环也会继续。一旦输入了有效的文件名，就可以使用break语句来解决这个问题，如下所示

if userInput == 'e':
    while True:
        path = input("Enter the text-file name to encrypt: ")
        if osp.exists(path):
             encrypt(path)
             print("Yeah!,1")
             break
        else:
            print("Sorry the file", path, "does NOT exist -- please try again!") 

在(D)项中，如果用户输入预先存在的文件的名称，则提供一个覆盖选项。但是，如果用户再次输入预先存在的文件的名称，您可以再次显示警告用户的消息。您可以通过将其放置在一个循环中来完成，如果用户允许继续重写文件，则在循环中执行break语句，如

elif userInput == 'd':
    path = input("Enter the text-file name to decrypt: ")
    if osp.exists(path):
        fileName,fileExtension = osp.split(path)
        fileName = fileName+".txt"
        print("Filename: ", fileName, "path: ", path)

        while osp.exists(fileName):
            print("WARNING: The file '%s' already exists!" %fileName)

            ch = input("Is it okay to wipe it out (y/n)? ")
            if ch == 'n':
                fileName = input("Enter the file name text that should be used (.txt extension will automatically be added) ")
                fileName = fileName + ".txt"
            elif ch == 'y':
                break 
        decrypt(path, fileName)

您可以将整个菜单驱动部分放在一个循环中，如

while True:
    userInput = input("Would you like to (e)ncrypt a file, (d)ecrypt a file, or e(x)it (enter e, d, or x)? ")
    while userInput not in validStrings:
        userInput = input("Sorry, that's an invalid choice. Please enter only e, d, or x: ")

    if userInput == 'e':
        while True:
            path = input("Enter the text-file name to encrypt: ")
            if osp.exists(path):
                 encrypt(path)
                 break
            else:
                print("Sorry the file", path, "does NOT exist -- please try again!") 

    elif userInput == 'd':
        path = input("Enter the text-file name to decrypt: ")
        if osp.exists(path):
            fileName,fileExtension = osp.split(path)
            fileName = fileName+".txt"
            print("Filename: ", fileName, "path: ", path)
            while osp.exists(fileName):
                print("WARNING: The file '%s' already exists!" %fileName)

                ch = input("Is it okay to wipe it out (y/n)? ")
                if ch == 'n':
                    fileName = input("Enter the file name text that should be used (.txt extension will automatically be added) ")
                    fileName = fileName + ".txt"
                elif ch == 'y':
                    break 
            decrypt(path, fileName)

    elif userInput == 'x':
        print("Program Complete!")
        return

将文件名拆分为其名称和扩展名时，请使用

fileName, fileExtension = osp.splitext(path)

而不是

fileName,fileExtension = osp.split(path)

如果path只存储文件的名称。

如果path是一条绝对路径或您可以做的事情

path,fullFileName = osp.split(path)
fileName, fileExtension = osp.splitext(fullFileName)

阅读关于splitext() 这里的文章。

Answer 2

好吧，在用户做出选择时，您似乎需要做一些修改。在这里，我修改了您的代码片段，只需看一看：

def main():
print("Welcome to the Vigenere-cipher Encryption/Decryption Program\n")
validStrings = ['e', 'd', 'x']
while True :
    userInput = input("Would you like to (e)ncrypt a file, (d)ecrypt a file, or e(x)it (enter e, d, or x)? ")
    if(userInput not in validStrings)
        userInput = input("Sorry, that's an invalid choice. Please enter only e, d, or x: ")
    elif : 
        if userInput == 'e':
            while True:
                path = input("Enter the text-file name to encrypt: ")
                if osp.exists(path):
                    encrypt(path)
                else:
                    print("Sorry the file", path, "does NOT exist -- please try again!")
            continue
        elif userInput == 'd':
            path = input("Enter the text-file name to decrypt: ")
            if osp.exists(path):
                fileName,fileExtension = osp.split(path)
                fileName = fileName+".txt"
                if osp.exists(fileName):
                    print("WARNING: The file '%s' already exists!" %fileName)

                    ch = input("Is it okay to wipe it out (y/n)? ")
                    if ch == 'n':
                        fileName = input("Enter the file name text that should be used (.txt extension will automatically be added) ")
                        fileName = fileName + ".txt"
                    elif ch == 'y':
                        pass
                decrypt(path, fileName)
            continue
        elif userInput == 'x':
            break
    print("Program Complete!")
    return

这里唯一的改变是，直到用户提供'x‘作为输入，而循环将不允许用户采取任何其他操作。

如果有用的话请告诉我。