title: Menu in python tkinter: save file to a new directory
body: <p>My python tkinter GUI program is writing a text file after doing some operations. I want to add a an export menu so that user can save this file into usb stick or in another directory. (I know we can do normal copy paste). But I would like to add this export menu. What I am trying to achieve is, When user clicks this export menu, the current directory should open, and the user can choose the file (myData.txt which is already being created and is present inside current directory) and user can now select a new directory and save the myData.txt in the new directory.  (it should work in Linux platform as well)</p>
  
  <pre><code>#My gui app creates a text file myData.txt in my current folder when I run the program. 
  
  from tkinter import *
  from tkinter import messagebox
  import sys
  
  def Export_File():
      #what do i need here???
  
  
  windows = Tk()
  menubar = Menu(windows)
  filemenu = Menu(menubar, tearoff=0)
  filemenu.add_command(label="Export", command =Export_File )
  
  filemenu.add_command(label="Exit", command=Exit_File)
  menubar.add_cascade(label="File", menu=filemenu)
  windows.configure(menu=menubar)
  
  
  windows.mainloop()
  </code></pre>