Simple tkinter script to open file and convert line endings to Windows style (CRLF)

convert2crlf.py

#!/usr/bin/python

import os

#TODO: What happens if script is imported as module?
WORKING_DIRECTORY = os.path.dirname(os.path.abspath(__file__))

from Tkinter import *
import tkFileDialog

class Application(Frame):

    def _fix_file(self, filename):
        f = open(filename, 'rU')
        t = f.read()
        t = t.replace('\n', '\r\n')
        f.close()
        f = open(filename, 'w')
        print repr(t)
        f.write(t)
        f.close()

    def add_files(self):
    
        files = tkFileDialog.askopenfilenames(initialdir=WORKING_DIRECTORY)
        fixed = []
        for f in files:
            self._fix_file(f)
            fixed.append(f)
            
        label = Label(self, text=('\n'.join(fixed)))
        label.pack(fill=X, expand=1)
    
    def __init__(self, master=None):
        
        Frame.__init__(self, master)
        
        master.title('eSIS to EasyGradePro')
        self['relief'] = RIDGE
        self['borderwidth'] = 2
        self.pack(fill=BOTH,expand=1)

        header = Label(self, text=('Fixed Files:\n\n'))
        header.pack()
        
        add_files_btn = Button(main, 
                               text='Fix more files', 
                               command=self.add_files)
        add_files_btn.pack({'side' : 'left'})
        
        close_btn = Button(main, text='Close', command=self.quit)
        close_btn.pack({'side' : 'right'})
        
        self.add_files()


if __name__ == '__main__':
    
    main = Tk()
    app = Application(master=main)
    app.mainloop()
    main.destroy()