协程和装饰器完成简易计算器

import functools as ft
import itertools as it

OPERATORS='+','-','/','*'
EXIT_COMMANDS='exit','quit'

#验证最近输入的三个数是否能构成计算公式
def can_calculate(state):
    if len(state)<3:
        return False
    *_,i1,op,i2=state       #unpack state并从倒数开始赋值，list的倒数第一个赋值给i2，倒数第二个赋值给op,倒数第三个赋值给i1，剩下的赋值给*_
    return isinstance(i1,float) and op in OPERATORS and isinstance(i2,float)

#计算
def calculate(state):
    *_,i1,op,i2=state
    if op=='+':
        result=i1+i2
    elif op=='-':
        result=i1-i2
    elif op=='/':
        result=i1/i2
    elif op=='*':
        result=i1*i2
    else:
        raise ValueError('Invalid operator!')
    print('%f %s %f=%f'%(i1,op,i2,result))
    return result

#验证输入是否合法
def validate_input(fnc):
    def inner():
        i=fnc()     #i=get_input()=input()
        try:
            i=float(i)
        except ValueError:
            pass
        if isinstance(i,float) or i in OPERATORS or i in EXIT_COMMANDS:
            return i
        return None

    return inner

#通过装饰器验证合法输入并返回
@validate_input
def get_input():    #get_input=validate_input(get_input)    i=get_input()=inner()
    return input()

def process_input():
    state=[]
    while True:
        update=yield
        state.append(update)      #state=[1，*，3，+，4]
        if can_calculate(state):
            result=calculate(state)
            state.append(result)    #state=[1，*,3,3，7]


#获取输入计算器的值并将值发送给process_input()函数
def calculator():
    g=process_input()
    g.send(None)
    while True:         #i=get_input()=inner()
        i=get_input()   #如果输入的值为非数字或则操作符验证器将返回None
        if i is None:
            print('Please enter a number or an operator')
            continue
        if i in EXIT_COMMANDS:
            break
        g.send(i)

calculator()

运行结果如下

3
*
5
3.000000 * 5.000000=15.000000
-
1
15.000000 - 1.000000=14.000000
/
3
14.000000 / 3.000000=4.666667
*
5
4.666667 * 5.000000=23.333333
*
6
23.333333 * 6.000000=140.000000
/
22
140.000000 / 22.000000=6.363636
exit