def _Button(self, text, file, command, extension='.gif'):
img_file = ("./res/button_images/" + file + extension)
im = PhotoImage(master=self, file=img_file)
b = Button(master=self,
text=text,
padx=2,
pady=2,
image=im,
command=command)
b._ntimage = im
b.pack(side=tkinter.LEFT)
return b
