## Order of flow in my simple calculator in Python

Please help... it might be something quick and easy I hope. I'm 9 days in to Python. I have code for a simple calculator. I cant figure out how to stop the calculator from seeking the values to be calculated if the selection of operations from the choices 1-4 is invalid to start with. If someone selects > 4 (from options 1,2,3,4) it returns 'Invalid input' but then proceeds to ask for value to calculate. How can I stop this from happening? It should cease after 'Invalid input' and be run again.

Here is the code:

#Simple calculator # define my simple functions def add(x, y): return x + y def min(x, y): return x - y def mul(x, y): return x * y def div(x, y): return x / y # provide options for operations print("Please select an operation.") print("For addition select 1. ") print("For subtraction select 2.") print("For multiplication select 3.") print("For division select 4.") option = input("Please enter the number of your option 1, 2, 3, 4:") # limit option to 1,2,3,4 if option > '4': print("Invalid input. Please select 1,2,3 or 4.") elif option < '5': print("Please select an operation.") print("For addition select 1. ") print("For subtraction select 2.") print("For multiplication select 3.") print("For division select 4.") num1 = float(input( "Please enter the first value: ")) num2 = float(input( "Please enter the second value: ")) if choice == '1': print(num1, " + ", num2, "=", add(num1,num2)) elif choice == '2': print(num1, " - ", num2, "=", min(num1, num2)) elif choice == '3': print(num1, " * ", num2, "=", mul(num1,num2)) elif choice =='4': print(num1, " / ", num2, "=", div(num1, num2))

One option is the use the exit command:

exit()

So that the program stops and should be restarted manually.

Another option is to use a while loop like this:

while option not in [1,2,3,4]: option = input("Please enter the number of your option 1, 2, 3, 4:")

This **forces** the user to use a valid input.

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You can put the input part in a while loop:

option = input("Please enter the number of your option 1, 2, 3, 4:") while option > '4': print("Invalid input. Please select 1,2,3 or 4.") option = input("Please enter the number of your option 1, 2, 3, 4:")

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