python ——计算器

from tkinter import *
import parser
from math import factorial

root = Tk()
root.title("计算器")

# i keeps the track of current position on the input text field
i = 0
# Receives the digit as parameter and display it on the input field
def get_variables(num):
    global i
    display.insert(i,num)
    i+=1

def clear_all():
    display.delete(0,END)

#add the input field
display = Entry(root)
display.grid(row=1,columnspan=6,sticky=N+E+S+W)

def get_operation(operator):
    global i
    length = len(operator)
    display.insert(i,operator)
    i+=length

#删除一个
def undo():
    entire_string = display.get()
    if len(entire_string):
        new_string = entire_string[:-1]
        clear_all()
        display.insert(0,new_string)
    else:
        clear_all()
        display.insert(0,"Error")

def calculate():
    entire_string = display.get()
    try:
        a = parser.expr(entire_string).compile()
        result = eval(a)
        clear_all()
        display.insert(0,result)
    except Exception:
        clear_all()
        display.insert(0,"Error")

def undo():
    entire_string = display.get()
    if len(entire_string):
        new_string = entire_string[:-1]
        clear_all()
        display.insert(0,new_string)
    else:
        clear_all()
        display.insert(0,"Error")

#Code to add buttons to the Calculator
#这里click函数就与button这个插件关联了，但是不好的地方就是不能传递参数。tkinter要求由按钮（或者其它的插件）
# 触发的控制器函数不能含有参数，
# 目的就是为了以统一的方式去调用他们。那么我们有什么办法给函数传递参数，因为这经常会用到。答案就是使用lambda。
Button(root,text="1",command=lambda: get_variables(1)).grid(row=2,column=0,sticky=N+S+E+W)
Button(root,text="2",command=lambda: get_variables(2)).grid(row=2,column=1,sticky=N+S+E+W)
Button(root,text="3",command=lambda: get_variables(3)).grid(row=2,column=2,sticky=N+S+E+W)

Button(root,text="4",command=lambda : get_variables(4)).grid(row=3,column=0,sticky=N+S+E+W)
Button(root,text="5",command=lambda: get_variables(5)).grid(row=3,column=1,sticky=N+S+E+W)
Button(root,text="6",command=lambda: get_variables(6)).grid(row=3,column=2,sticky=N+S+E+W)

Button(root,text="7",command=lambda : get_variables(7)).grid(row=4,column=0,sticky=N+S+E+W)
Button(root,text="8",command=lambda: get_variables(8)).grid(row=4,column=1,sticky=N+S+E+W)
Button(root,text="9",command=lambda: get_variables(9)).grid(row=4,column=2,sticky=N+S+E+W)

#添加清除所有按钮
Button(root,text="AC",command=lambda: clear_all()).grid(row=5,column=0,sticky=N+S+E+W)
Button(root,text="0",command=lambda: get_variables(0)).grid(row=5,column=1,sticky=N+S+E+W)
Button(root,text=".",command=lambda: get_variables(".")).grid(row=5,column=2,sticky=N+S+E+W)


Button(root,text="+",command= lambda :get_variables("+")).grid(row=2,column=3, sticky=N+S+E+W)
Button(root,text="-",command= lambda :get_operation("-")).grid(row=3,column=3, sticky=N+S+E+W)
Button(root,text="*",command= lambda :get_operation("*")).grid(row=4,column=3, sticky=N+S+E+W)
Button(root,text="/",command= lambda :get_operation("/")).grid(row=5,column=3, sticky=N+S+E+W)

# adding new operations
Button(root,text="pi",command= lambda :get_operation("*3.14")).grid(row=2,column=4, sticky=N+S+E+W)
Button(root,text="%",command= lambda :get_operation("%")).grid(row=3,column=4, sticky=N+S+E+W)
Button(root,text="(",command= lambda :get_operation("(")).grid(row=4,column=4, sticky=N+S+E+W)
Button(root,text="exp",command= lambda :get_operation("**")).grid(row=5,column=4, sticky=N+S+E+W)
 
Button(root,text="<-",command= lambda :undo()).grid(row=2,column=5, sticky=N+S+E+W)
Button(root,text="x!", command= lambda: fact()).grid(row=3,column=5, sticky=N+S+E+W)
Button(root,text=")",command= lambda :get_operation(")")).grid(row=4,column=5, sticky=N+S+E+W)
Button(root,text="^2",command= lambda :get_operation("**2")).grid(row=5,column=5, sticky=N+S+E+W)
Button(root,text="^2",command= lambda :get_operation("**2")).grid(row=5,column=5, sticky=N+S+E+W)
Button(root,text="=",command= lambda :calculate()).grid(columnspan=6, sticky=N+S+E+W)

root.mainloop()