calc.py

def add(x,y):
    return x+y
def subtract(x,y):
    return x-y
def multiply(x,y):
    return x*y
def divide(x,y):
    return t/y
print("select operations.")
print("1.Add")
print("2.subtract")
print("3.multiply")
print("4.divide")
while True:
    choice=input("Enter choice(1/2/3/4): ")
    if choice in('1','2','3','4'):
    
        try:
            num1=float(input("enter first number: "))
            num2=float(input("enter second number: "))
        except ValueError:
            print("invalid input.Please enter a number.")
            continue
        if choice == "1":
            print(num1,"+",num2 ,"=",add(num1,num2))
        elif choice == "2":
            print(num1,"-",num2 , "=",subtract(num1,num2))
        elif choice == "3":
            print(num1,"x",num2 ,"=",multiply(num1,num2))
        elif choice == "4":
            print(num1,"/",num2 ,"=",division(num1,num2)) 
        next_calculation=input("let's do next calculation?(yes/no): ")
        if next_calculation == "no":
            break
    else:
        print("invalid input")