只获取一次循环返回的值到 print()

Question

When trying to retrieve the decrypted password for the second choice, I can't keep the program from printing Does Not Compute no matter whether the website entered is true or not. It prints twice when it is untrue so this leads me to believe the it's printing for i in the range(len(passwords)) which is 2.

How do I get it to print just the password or Does Not Compute once and not have it iterate again? I'm trying to check if the input is equal to the website but it still prints iterates twice.

import csv
import sys

# The password list - We start with it populated for testing purposes
passwords = [["yahoo", "XqffoZeo"], ["google", "CoIushujSetu"]]
# The password file name to store the passwords to
passwordFileName = "samplePasswordFile"
# The encryption key for the caesar cypher
encryptionKey = 16
# Caesar Cypher Encryption
def passwordEncrypt(unencryptedMessage, key):
    # We will start with an empty string as our encryptedMessage
    encryptedMessage = ""
    # For each symbol in the unencryptedMessage we will add an encrypted symbol into the encryptedMessage
    for symbol in unencryptedMessage:
        if symbol.isalpha():
            num = ord(symbol)
            num += key
            if symbol.isupper():
                if num > ord("Z"):
                    num -= 26
                elif num < ord("A"):
                    num += 26
            elif symbol.islower():
                if num > ord("z"):
                    num -= 26
                elif num < ord("a"):
                    num += 26
            encryptedMessage += chr(num)
        else:
            encryptedMessage += symbol
    return encryptedMessage


def loadPasswordFile(fileName):
    with open(fileName, newline="") as csvfile:
        passwordreader = csv.reader(csvfile)
        passwordList = list(passwordreader)
    return passwordList


def savePasswordFile(passwordList, fileName):
    with open(fileName, "w+", newline="") as csvfile:
        passwordwriter = csv.writer(csvfile)
        passwordwriter.writerows(passwordList)


prompt_msg = """
What would you like to do:
 1. Open password file
 2. Lookup a password
 3. Add a password
 4. Save password file
 5. Print the encrypted password list (for testing)
 6. Quit program
Please enter a number (1-4)
"""

while True:
    print(prompt_msg)
    choice = input()

    if choice == "1":  # Load the password list from a file
        passwords = loadPasswordFile(passwordFileName)

    elif choice == "2":  # Lookup at password
        print("Which website do you want to lookup the password for?")
        for keyvalue in passwords:
            print(keyvalue[0])
        print("----")
        passwordToLookup = input()
        for i in range(len(passwords)):
            print(f"i={i}, store_info={passwords[i]}, website={passwords[i][0]}")
            if passwordToLookup == passwords[i][0]:
                password = passwordEncrypt(passwords[i][1], -(encryptionKey))
                print(f"=> The password is {password}.")
            else:
                print("=> Does not compute!")

    elif choice == "3":
        print("What website is this password for?")
        website = input()
        print("What is the password?")
        unencryptedPassword = input()
        unencryptedPassword = passwordEncrypt(unencryptedPassword, encryptionKey)
        newList = [website, unencryptedPassword]
        passwords.append(newList)
        print("Your password has been saved.")

    elif choice == "4":  # Save the passwords to a file
        savePasswordFile(passwords, passwordFileName)

    elif choice == "5":  # print out the password list
        for keyvalue in passwords:
            print(", ".join(keyvalue))

    elif choice == "6":  # quit our program
        sys.exit()

    print()
    print()
    ####### YOUR CODE HERE ######
    # You will need to find the password that matches the website
    # You will then need to decrypt the password
    #
    # 1. Create a loop that goes through each item in the password list
    #  You can consult the reading on lists in Week 5 for ways to loop through a list
    #
    # 2. Check if the name is found.  To index a list of lists you use 2 square backet sets
    #   So passwords[0][1] would mean for the first item in the list get it's 2nd item (remember, lists start at 0)
    #   So this would be 'XqffoZeo' in the password list given what is predefined at the top of the page.
    #   If you created a loop using the syntax described in step 1, then i is your 'iterator' in the list so you
    #   will want to use i in your first set of brackets.
    #
    # 3. If the name is found then decrypt it.  Decrypting is that exact reverse operation from encrypting.  Take a look at the
    # caesar cypher lecture as a reference.  You do not need to write your own decryption function, you can reuse passwordEncrypt
    #
    #  Write the above one step at a time.  By this I mean, write step 1...  but in your loop print out every item in the list
    #  for testing purposes.  Then write step 2, and print out the password but not decrypted.  Then write step 3.  This way
    #  you can test easily along the way.
    #

Answer 1

It seems like you want to print does not compute only if NONE of the stored passwords match the input; but as it is, you're printing that message for EACH password that doesn't match (even if some other password did match).

I've modified your loop to break when a match is found, and only print the message if no matches were found (by adding an else clause to the for loop, which executes only if the loop makes it all the way to the end.)

    passwordToLookup = input()
    for i in range(len(passwords)):
        if passwordToLookup == passwords[i][0]:
            webSite = passwordEncrypt(passwords[i][1],-(encryptionKey))
            print()
            print('The password is ' + webSite+'.')
            print(i)
            print(passwords[i])
            print(passwords[i][0])
            break
    else:
        # if we got to the end of the loop, no passwords matched
        print('Does not compute!')

Answer 2

First, I took the liberty to reformat and improve your code to look a bit nicer.

• Multi-line string for the prompt
• F-string to print variables (Python 3.4 and above)
• Formatting with the new black module

Your problem is that you loop through all the stored websites

    for i in range(len(passwords)):
        if passwordToLookup == passwords[i][0]:
            ...
        else:
            ...

Actually what you should do is

1. Checking if the website exists in the current list
2. Return decrypted password if found, and Cannot computer otherwise

The best way to do 1. is to:

• Transform the tuples of passwords to a dictionary: passwords = {"yahoo":"XqffoZeo", "google":"CoIushujSetu"}
• Check if website is one of the keys: if website in passwords.keys(): ...
• Update the rest of the code accordingly (as the list of passwords is not a list of tuples but a dictionary)

Or more simply: just transform the list of tuples to a dictionary when extracting the password:

elif choice == "2":  # Lookup at password
    print("Which website do you want to lookup the password for?")
    for keyvalue in passwords:
        print(keyvalue[0])
    print("----")
    passwordToLookup = input()
    dict_passwords = dict(passwords)
    if passwordToLookup in dict_passwords:
        encrypted = dict_passwords[passwordToLookup]
        password = passwordEncrypt(encrypted, -(encryptionKey))
        print(f"=> The password is {password}.")
    else:
        print("=> Does not compute!")