Coroutines and decorators complete the easy calculator

1  import functools as ft
 2  import itertools as it
 3  
4 OPERATORS= ' + ' , ' - ' , ' / ' , ' * ' 
5 EXIT_COMMANDS= ' exit ' , ' quit ' 
6  
7  #Verify whether the last three numbers entered are not Can form calculation formula 
8  def can_calculate(state):
 9      if len(state)<3 :
 10          return False
 11     *_,i1,op,i2=state        # unpack state and assign values ​​from the bottom, the last one of the list is assigned to i2, the second last is assigned to op, the third last is assigned to i1, and the rest are assigned to *_ 
12      return isinstance(i1,float) and op in OPERATORS and isinstance(i2,float)
 13  
14  #Calculate 15 def calculate 
(state):
 16      *_,i1,op,i2= state
 17 if op== ' + ' :
 18          result=i1+ i2
 19 elif op== ' - ' :
 20          result=i1- i2
           21      elif op== ' / ' :
 22          result=i1/ i2
 23      elif op== ' * ' :
 24          result=i1* i2
 25      else :
 26          raise ValueError( ' Invalid operator! ' )
 27      print ( ' %f % s %f=%f ' % (i1,op,i2,result))
 28      return result
 29  
30  #Validate whether the input is legal 
31  def validate_input(fnc):
32      def inner():
 33          i=fnc()      # i=get_input()=input() 
34          try :
 35              i= float(i)
 36          except ValueError:
 37              pass 
38          if isinstance(i,float) or i in OPERATORS or i in EXIT_COMMANDS:
 39              return i
 40          return None
 41  
42      return inner
 43  
44  #Validate valid input through the decorator and return 
45  @validate_input
46 def get_input():    #get_input=validate_input(get_input)    i=get_input()=inner()
47     return input()
48 
49 def process_input():
50     state=[]
51     while True:
52         update=yield
53         state.append(update)      #state=[1，*，3，+，4]
54         if can_calculate(state):
55             result=calculate(state)
56             state.append(result)    #state=[1，*,3,3，7]
57 
58 
59 #Get the value of the input calculator and send the value to the process_input() function 
60  def calculator():
 61      g= process_input()
 62      g.send(None)
 63      while True:          # i=get_input()=inner() 
64          i=get_input() #If    the input value is not a number or the operator validator will return None 
65          if i is None:
 66              print ( ' Please enter a number or an operator ' )
 67              continue 
68          if i in EXIT_COMMANDS:
 69              break 
70         g.send(i)
71 
72 calculator()

The running result is as follows

 1 3
 2 *
 3 5
 4 3.000000 * 5.000000=15.000000
 5 -
 6 1
 7 15.000000 - 1.000000=14.000000
 8 /
 9 3
10 14.000000 / 3.000000=4.666667
11 *
12 5
13 4.666667 * 5.000000=23.333333
14 *
15 6
16 23.333333 * 6.000000=140.000000
17 /
18 22
19 140.000000 / 22.000000=6.363636
20 exit