如何修复IndexError：列表索引超出范围

Question

我希望它加密一条消息，但是它只说是一个错误：

  

第47行，在       加密= swap_letters（消息）

     

第27行，在swap_letters中       letter_list.append（odd_letters [counter]）   IndexError：列表索引超出范围

def swap_letters(message) :
    letter_list = []
    if not is_even( len ( message ) ) :
        message = message+"x"
    even_letters = get_even_letters( message )
    odd_letters = get_odd_letters( message )
    for counter in range( 0, int( len( message )/2 )-1 ):
        letter_list.append(odd_letters[counter])
        letter_list.append(even_letters[counter])
    new_message = ' '.join(letter_list)
    return new_message


while True:
    task = get_task()
    if task == "encrypt":
        message = get_message()
        encrypted = swap_letters(message)
        messagebox.showinfo("Message encrypted is: ", encrypted)
    elif task == "decrypt":
        message = get_message()
        decrypted = swap_letters(message)
        messagebox.showinfo("Plaintext of the message is: ", decrypted)
    else:
        break
root.mainloop()

完整代码

from tkinter import messagebox, simpledialog, Tk

def is_even(number):
    return number % 2 ==0

def get_even_letters(message):
    even_letters = []
    for counter in range(0, len(message)):
        if is_even(counter):
            even_letters.append(message[counter])
    return even_letters

def get_odd_letters(message):
    odd_letters = []
    for counter in range(0, len(message)):
        if not is_even(counter):
            odd_letters.append(message[counter])
    return odd_letters

def swap_letters(message) :
    letter_list = []
    if not is_even( len ( message ) ) :
        message = message+"x"
    even_letters = get_even_letters( message )
    odd_letters = get_odd_letters( message )
    for counter in range( 0, int( len( message )/2 ) ):
        letter_list.append(odd_letters[counter])
        letter_list.append(even_letters[counter])
    new_message = ' '.join(letter_list)
    return new_message

def get_task():
    task=simpledialog.askstring("Task","Do you want to encrypt or decrypt?")
    return task

def get_message():
    message=simpledialog.askstring("Message","Enter your message")
    return message

root = Tk()
root.withdraw()

while True:
    task = get_task()
    if task == "encrypt":
        message = get_message()
        encrypted = swap_letters(message)
        messagebox.showinfo("Message encrypted is: ", encrypted)
    elif task == "decrypt":
        message = get_message()
        decrypted = swap_letters(message)
        messagebox.showinfo("Plaintext of the message is: ", decrypted)
    else:
        break
root.mainloop()

我希望它对短语进行打乱，但是它显示IndexError：列表索引超出范围