calculator demo

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)