Calculator(+,-,*,/)

def check_value(x):
    try:
        return True,float(x)
    except ValueError:
        print("Data Error")
        return None
def check_op(op):
    if op in ['*','/','+','-']:
        return op
    else:
        print("Operator Error")
def calc(x,y,op):
    if check_value(x)[0] and check_value(y)[0] and check_op(op):
        x = check_value(x)[1];y = check_value(y)[1]
        if op == "*":
            return x*y
        elif op == "+":
            return x+y
        elif op == "-":
            return x-y
        else:
            if y == 0:
                print("second operand can not be zero")
                return None
            else:
                return x/y
exp = input("Please input expression with space between :\n").split()
print(exp)
while len(exp)%2 and len(exp) >= 3:
    if len(exp)==3 or exp[3] in ["+","-"] or exp[1] in ['*','/']:
        result = calc(exp[0],exp[2],exp[1])
        exp[:3] = [result]
        print(exp)
    else:
        result = calc(exp[2],exp[4],exp[3])
        exp[2:5] = [result]
        print(exp)
else:
    if (len(exp)%2==0):
        print("wrong expression")
    else:
        print(exp[0])