一个简易计算器：

# coding:utf-8
import traceback
from tkinter import Tk
from tkinter import Text
from tkinter import Label
from tkinter import Button
from tkinter import Entry
from tkinter import StringVar
from tkinter import N, S, W, E, END, DISABLED, RAISED, RIGHT
from functools import partial

def get_input(entry, arg):
    """insert char"""
    entry.insert(END, arg)

def backspace(entry):
    """delete char"""
    input_len = len(entry.get())
    entry.delete(input_len - 1)

def clear(entry):
    """clear entry"""
    entry.delete(0, END)

def calc(entry, var):
    """figure out expression"""
    text = entry.get()
    try:
        output = str(eval(text.strip()))
    except SyntaxError:
        output = 'SyntaxError'
    except ZeroDivisionError:
        output = 'ZeroDivisionError'
    clear(entry)
    var.set(output)

def invoke(button):
    button.config(state='active')
    button.invoke()

def cal():
    """main widget"""
    root = Tk()
    root.title("Calc")
    root.resizable(0, 0)

    var = StringVar()
    var.set('')

    label = Label(root, textvariable=var, anchor='e', width=30, font=("Arial", 16))
    label.grid(row=0, column=0, columnspan=4, sticky='nwse', padx=5, pady=2)

    entry = Entry(root, justify="right")
    entry.grid(row=1, column=0, columnspan=4, sticky='nwse', padx=5, pady=10)

    button_bg = '#e0f0e0'
    button_active_bg = '#f0e0f0'

    my_button = partial(
        Button, root, bg=button_bg, activebackground=button_active_bg, font=("Arial", 12))

    button_list = [
        ('7', '<Key-7>', '<KeyRelease-7>'),
        ('8', '<Key-8>', '<KeyRelease-8>'),
        ('9', '<Key-9>', '<KeyRelease-9>'),
        ('+', '<plus>', '<KeyRelease-plus>'),
        ('4', '<Key-4>', '<KeyRelease-4>'),
        ('5', '<Key-5>', '<KeyRelease-5>'),
        ('6', '<Key-6>', '<KeyRelease-6>'),
        ('-', '<minus>', '<KeyRelease-minus>'),
        ('1', '<Key-1>', '<KeyRelease-1>'),
        ('2', '<Key-2>', '<KeyRelease-2>'),
        ('3', '<Key-3>', '<KeyRelease-3>'),
        ('*', '<asterisk>', '<KeyRelease-asterisk>'),
        ('0', '<Key-0>', '<KeyRelease-0>'),
        ('0', '<Key-0>', '<KeyRelease-0>'),
        ('.', '<period>', '<KeyRelease-period>'),
        ('/', '<slash>', '<KeyRelease-slash>'),
        ('<-', '<BackSpace>', '<KeyRelease-BackSpace>'),
        ('C', '<Delete>', '<KeyRelease-Delete>'),
        ('=', '<Return>', '<KeyRelease-Return>'),
        ('=', '<Return>', '<KeyRelease-Return>'),
        ]

    for i, text in enumerate(button_list):
        text, key, key_release = text
        if i == 13 or i == 19:
            continue

        row = (i // 4 + 2)
        column = (i % 4)
        columnspan = None
        command = lambda text=text: get_input(entry, text)

        if i == 12 or i == 18:
            columnspan = 2
        if text == '<-':
            command = lambda: backspace(entry)
        elif text == 'C':
            command = lambda: clear(entry)
        elif text == '=':
            command = lambda: calc(entry, var)

        but = my_button(text=text, command=command)
        e_press_command = lambda event, text=text, but=but: invoke(but)
        e_release_command = lambda event, text=text, but=but: but.config(state='normal')
        root.bind(key, e_press_command)
        root.bind(key_release, e_release_command)
        but.grid(
            row=row,
            column=column,
            columnspan=columnspan,
            padx=3,
            pady=5,
            sticky=E + W)

    root.mainloop()

if __name__ == '__main__':
    cal()