result = None
ls = input（please input a number:")
#ls = '1 + 1 + 1 + 1 + 'in terminal only happens in VS Code
ls = ls.split()
def check_float(data):
try:
float (data)
return True
except ValueError:
print ('invalid input')
return False
while (len(ls) >=3):
x = ls[0]
op = ls [1]
y = ls [2]
if type(float(x)) == float and type (float(y)) == float:
x = float(x)
y = float (y)
if op in ['+', '-', '*' ,'/']:
if op == '+':
result = x + y
if op == '-':
result = x - y
if op == '*':
result = x * y
if op == '/':
result = x / y
else:
print ('wrong operator')
break
else:
print ('wrong operand')
break
del ls[:2]
ls[0] = result
if len(ls) == 2:
print ('wrong operands')
break
if len(ls) == 1:
break
print(result)
