#myfirstgame.py

APP_TITLE="Data's First \"Game\""
import windows
import client, footer

#client.py
import myfirstgame, pygame, os, sys, windows
from myfirstgame import *
from pygame.locals import *

datafiles=["","grass.png","human_male.png","human_female.png","icon.png"]
for data in datafiles:
	if not os.access(os.path.join("data",data),os.R_OK):
		err=windows.tkError(master=tkroot,msg="Could not locate the file \""+data+"\" in the data directory.") #error line: AttributeError
		err.master.title(APP_TITLE)
		err.mainloop()
		sys.exit(0)

... #everything irrelevant

#windows.py

import myfirstgame
from myfirstgame import *
from Tkinter import *

class tkError(Frame):
    def createWidgets(self):
	self.MSG = Label(self)
	self.MSG["text"]=self.msg
	self.MSG.pack({"side": "top"})

        self.QUIT = Button(self)
        self.QUIT["text"] = "OK"
        self.QUIT["command"] =  self.quit

        self.QUIT.pack({"side": "bottom"})
    def __init__(self, master=None, msg=None):
	self.msg=msg
        Frame.__init__(self, master)
        self.pack()
        self.createWidgets()

tkroot = Tk()

#footer.py
import myfirstgame, windows
from myfirstgame import *
windows.tkroot.destroy()