cryptography issue #7847

hello.py

from cryptography.fernet import Fernet
from tkinter import *

class Application(Frame):
    def encrypt(self):
        if not self.encrypted:
            self.message = self.fernet.encrypt(self.message.encode()).decode()
            self.encrypted = True
            self.labeltext.set(self.message)

    def decrypt(self):
        if self.encrypted:
            self.message = self.fernet.decrypt(self.message).decode()
            self.encrypted = False
            self.labeltext.set(self.message)

    def createWidgets(self):

        frame1 = Frame(self)
        frame1.pack(fill=X)

        self.labeltext = StringVar()
        self.labeltext.set(self.message)
        self.label = Label(frame1, textvariable=self.labeltext)
        self.label.pack(fill=X, padx=100)

        frame2 = Frame(self)
        frame2.pack(fill=X)

        self.QUIT = Button(frame2, text="Quit", command=self.quit)
        self.QUIT.pack({"side": "left"})

        self.encrypt = Button(frame2, text="Encrypt", command=self.encrypt)
        self.encrypt.pack({"side": "left"})

        self.decrypt = Button(frame2, text="Decrypt", command=self.decrypt)
        self.decrypt.pack({"side": "left"})

    def __init__(self, master=None):
        self.message = "Some Text"
        self.encrypted = False

        key = Fernet.generate_key()
        self.fernet = Fernet(key)

        Frame.__init__(self, master)
        self.pack()
        self.createWidgets()

app = Application()
app.mainloop()

setup.py

"""
Script for building the example.

Usage:
    python setup.py py2app
"""
from setuptools import setup

setup(
    app=['hello.py'],
    setup_requires=["py2app"],
    options={'py2app': {'includes': {'cffi'}}}
)