有哪位能帮我看一下代码？

from tkinter import Tk,simpledialog,messagebox
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(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(map(str,letter_list))
        return new_message
def get_task():
    task=simpledialog.askstring('任务','你想加密还是解密？')
    return task
def get_message():
    message=simpledialog.askstring('消息','输入机密消息(提示:请输入英文):')
    return message
root=Tk()
root.withdraw()
while True:
    task=get_task()
    if task=='加密':
        message=get_message()
        encrypted=swap_letters(message)
        messagebox.showinfo('机密消息的密文是:',encrypted)
    elif task=='解密':
        message = get_message()
        decrypted=swap_letters(message)
        messagebox.showinfo('机密消息的明文是:',decrypted)
    else:
        break
root.mainloop()

链接: https://pan.baidu.com/s/10ND2OnDD7i9Z7qKK7_Yyvw 提取码：qji3

你的问题是？报错了？

链接: https://pan.baidu.com/s/10ND2OnDD7i9Z7qKK7_Yyvw 提取码：qji3