Tkinter __call__

[Gigs_]

from Tkinter import *
from tkFileDialog   import askopenfilename
from tkColorChooser import askcolor
from tkMessageBox   import askquestion, showerror
from tkSimpleDialog import askfloat

demos = {
     'Open':  askopenfilename,
     'Color': askcolor,
     'Query': lambda: askquestion('Warning', 'You typed 		 
"..."\nConfirm?'),
     'Error': lambda: showerror('Error!', "He's dead, Jim"),
     'Input': lambda: askfloat('Entry', 'Enter credit card number')
}


class Demo(Frame):
     def __init__(self, parent=None):
         Frame.__init__(self, parent)
         self.pack()
         Label(self, text="Basic demos").pack()
         for (key, value) in demos.items():
             func = (lambda key=key: self.printit(key))
             Button(self, text=key, command=func).pack(side=TOP, fill=BOTH)
     def printit(self, name):
         print name, 'returns =>', demos[name]()


I have tried but cant get it to work properly.
I want to instead printit method to put __call__ and call it like that
Can someone help me, please?