How to restart a programm if input is invalid python

first project beginner here! I just finished my first project, a somewhat working calculator i know it is not that great but as i said beginner. I would like to limit the options for number = input meaning if you write anything else than add,substract,divide or multiply you receive an error like " please try again" and afterwards the programm is restarted

Help very much appreciated Thank you.

list = ("add", "substract", "divide" , "multiply" )

number = input("do you want to add substract divide or multiply? ")

if number in list:
    print("ok")
else:
    print("try again")

number_one = float(input("enter your first number "))
number_two = float(input("enter your second number "))

if number == "add":
    solution_one = number_one + number_two
    print(solution_one)

if number == "substract":
    solution_two = number_one - number_two
    print(solution_two)

if number == "divide":
    solution_three = number_one / number_two
    print(solution_three)

if number == "multiply":
    solution_four = number_one * number_two
    print(solution_four)

i could only find solutions regarding while loops but i did not know how to use them in this case as these weren't strings but integers.

The fact that you're prompting for a string doesn't change the way the while loop works. Run your code in a loop and break when it's time for the loop to end.

while True:
    number = input("do you want to add substract divide or multiply? ")
    if number in ("add", "substract", "divide" , "multiply" ):
        print("ok")
        break
    print("try again")

Note that it's considered bad practice to give a variable a name like list (or any other built-in name) since it can lead to very confusing bugs when you try to reference the built-in name later!

You could consider using the operator module.

Build a dictionary that maps the user's selected operation with the relevant function.

import operator

OMAP = {
    'add': operator.add,
    'subtract': operator.sub,
    'divide': operator.truediv,
    'multiply': operator.mul
    }


while (op := input('Do you want to add, subtract, multiply, divide or end? ')) != 'end':
    try:
        if (func := OMAP.get(op)):
            x = float(input('Enter your first number: '))
            y = float(input('Enter your second number: '))
            print(func(x, y))
        else:
            raise ValueError(f'"{op}" is not a valid choice')
    except ValueError as e:
        print(e)