problems with the Return function

Question

I’m trying to make a program where the person has to write a number, but when she writes a number that doesn’t fit the requirements she has to write another.

I can’t use the function return correctly:

def pergunta():
    t = int(input('digite um numero: '))
    dois = t<3
    if dois:
        print ('tente outro')
        return t
    else:
        print ('esse numero ai, parabéns')

pergunta()

Answer 1

return closes the execution of the. That is, if the code gets there in the return, it exits the function and does not perform anything else that is within the function.

If you want to repeat something, use a simple loop:

def pergunta():
    while True:
        t = int(input('digite um numero: '))
        if t < 3:
            print ('tente outro')
        else:
            print ('esse numero ai, parabéns')
            return t
 
pergunta()

Thus, if the typed number is invalid, it asks for another to be typed. If valid, the function returns the value.

One detail is that you’re not using the payback for anything, maybe you should do something like valor = pergunta() and then use the valor in the rest of the programme.

---

The other answer suggested using recursion, which even "works", but is not the best option. This is because each recursive call takes up space on the runstack, and if many invalid numbers are typed, a pile burst (see here - go to the bottom of the page and see the error).

Already using while, only one call is made and the stack overflow does not occur, regardless of how many invalid numbers are entered.

Answer 2

First you have to understand that return is a reserved python word, which serves to return a value and terminate the function. So the return is executed, the function to. Therefore, its function pergunta() will ask for an integer number and save it in the variable t, if that number is less than 3, the function will print tente outro on the screen, will return the value of t and end the execution. However, this returned value is not being stored in any corner, so it is lost. If you want the function to run again, instead of terminating, remove the return, replacing it with a recursive call. So:

def pergunta():
    t = int(input('digite um numero: '))
    dois = t<3
    if dois:
        print ('tente outro')
        pergunta()
    else:
        print ('esse numero ai, parabéns')

pergunta()

The difference here is that when the if dois is executed, the printa function tente outro on the screen and calls itself. That is, the function is executed by itself, this is what is called recursiveness. Now let’s better understand the workings of return. As already said, it terminates the function and returns a value, consider the example:

def pergunta():
    t = int(input('digite um numero: '))
    dois = t<3
    if dois:
        print ('valor menor que 3')
        return t
    else:
        print ('valor maior ou igual a 3')
        return t

pergunta()

A simple program that collects a value, tells whether it is less than three and returns the said value. The question here is, if it returns a value, where is it stored? Well, this should be specified in the code. Imagine a program consisting of a single line of code:

4

This program does absolutely nothing. If we want to store that value somewhere, ideally:

algumLugar = 4

The same goes for the functions, if we want to store the function return pergunta() somewhere, we should, rather than:

pergunta()

Use:

retorno = pergunta()

So the value of t, which is what the function returns, will be stored in the variable retorno, and to see this value, just add a print(retorno)