{{{
#!python

#!/usr/bin/env python
# -*- coding: cp1252 -*-
"""
Calculadora com GUI em Tkinter, utilizando funções internas do Python
Baseada na implementação de Mark Lutz em "Programming Python", pág. 675

Autor deste script: Jean-Guy Schneider <schneidr@iam.unibe.ch>
Última modificação Mon Jun 22 17:36:02 MET DST 1998
"""
from Tkinter import *

class CalcGUI (Frame):
    """
    class 'CalcGUI': a simple calculator
    """
    
    def __init__ (self, master=None):
	Frame.__init__ (self, master)
	self.pack (expand=YES, fill=BOTH)
	self.master.title ('Python Calculator')
	self.master.iconname ("pcalc")

	self._names = {}                  # private namespace for expressions

	self._text = Text (self, width=16, height=1)     # a text widget
	self._text.pack (expand=YES, fill=X)             # as display

	rows = ["abcd", "0123", "4567", "89()"]          # buttons
	for row in rows:
	    frm = Frame (self)                           # into separate frame
	    for char in row:
		but = Button (frm, text=char,
			      command=lambda s=self, y=char: s._append (y))
		but.pack (side=LEFT, expand=YES, fill=X)
	    frm.pack (expand=YES, fill=X)

	frm2 = Frame (self)
	for char in "+-*/=":                             # operators
	    but = Button (frm2, text=char,
			  command=lambda s=self, y=char: s._append (' '+y+' '))
	    but.pack (side=LEFT, expand=YES, fill=X)
	frm2.pack (expand=YES, fill=X)

	frm3 = Frame (self)                               # command buttons
	but = Button (frm3, text='eval', command=lambda s=self: s.eval ())
	but.pack (side=LEFT, expand=YES, fill=X)
	but = Button (frm3, text='clear', command=lambda s=self: s._clear ())
	but.pack (side=LEFT, expand=YES, fill=X)
	but = Button (frm3, text='exit', command=self.quit)
	but.pack (side=LEFT, expand=YES, fill=X)
	frm3.pack (expand=YES, fill=X)

    def eval (self):
	try:
	    cont = self._get()                           # get contents
	    self._clear()                                # clear text widget
	                                                 # eval as expression
	    self._append (`eval (cont, self._names, self._names)`)
	except SyntaxError:
	    try:
		exec (cont, self._names, self._names)    # exec as statement
	    except:
		self._append ("ERROR")
	    else:
		self._clear()                            # worked as statement
	except:
	    self._append ("ERROR")                       # other errors

    # private helper functions: text widget manipulation
    def _clear (self):
	"""Clear text widget"""
	self._text.delete ('1.0', '2.0')

    def _append (self, text):
	"""Append 'text' to text widget"""
	self._text.insert ('1.end', text)

    def _get (self):
	"""get contents of text widget"""
	return self._text.get ('1.0', '1.end')

if __name__ == '__main__':
    CalcGUI().mainloop()

}}}