button_clear = tk.Button(root, text='C', width=5, font=('宋体', 16), relief='flat', background='#C0C0C0', command=lambda: clear())
button_back = tk.Button(root, text='←', width=5, font=('宋体', 16), relief='flat', background='#C0C0C0', command=lambda: back())
button_division = tk.Button(root, text='/', width=5, font=('宋体', 16), relief='flat', background='#C0C0C0', command=lambda: operator('/'))
button_multiplication = tk.Button(root, text='x', width=5, font=('宋体', 16), relief='flat', background='#C0C0C0', command=lambda: operator('*'))
button_clear .grid(padx=4, row=1, column=0)
button_back .grid(padx=4, row=1, column=1)
button_division .grid(padx=4, row=1, column=2)
button_multiplication .grid(padx=4, row=1, column=3)
button_seven = tk.Button(root, text='7', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('7'))
button_eight = tk.Button(root, text='8', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('8'))
button_nine = tk.Button(root, text='9', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('9'))
button_subtraction = tk.Button(root, text='—', width=5, font=('宋体', 16), relief='flat', background='#C0C0C0', command=lambda: operator('-'))
button_seven .grid(padx=4, row=2, column=0)
button_eight .grid(padx=4, row=2, column=1)
button_nine .grid(padx=4, row=2, column=2)
button_subtraction .grid(padx=4, row=2, column=3)
button_four = tk.Button(root, text='4', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('4'))
button_four.grid(padx=4, pady=4, row=3, column=0)
button_five = tk.Button(root, text='5', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('5'))
button_five.grid(padx=4, row=3, column=1)
button_six = tk.Button(root, text='6', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('6'))
button_six.grid(padx=4, row=3, column=2)
button_addition = tk.Button(root, text='+', width=5, font=('宋体', 16), relief='flat', background='#C0C0C0', command=lambda: operator('+'))
button_addition.grid(padx=4, row=3, column=3)
button_one = tk.Button(root, text='1', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('1'))
button_one.grid(padx=4, row=4, column=0)
button_two = tk.Button(root, text='2', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('2'))
button_two.grid(padx=4, row=4, column=1)
button_three = tk.Button(root, text='3', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('3'))
button_three.grid(padx=4, row=4, column=2)
button_equal = tk.Button(root, text='=', width=5, height=3, font=('宋体', 16), relief='flat', background='#C0C0C0', command=lambda: equal())
button_equal.grid(padx=4, row=4, rowspan=5, column=3)
button_zero = tk.Button(root, text='0', width=12, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('0'))
button_zero.grid(padx=4, pady=4, row=5, column=0, columnspan=2)
button_decimal = tk.Button(root, text='.', width=5, font=('宋体', 16), relief='flat', background='#FFDEAD', command=lambda: append_num('.'))
button_decimal.grid(padx=4, row=5, column=2)