Restart application in Python

If you want to request the data again it would look like this:

while True: #inicia o laço
    cpf = input('Digite os nove primeiros dígitos do CPF: ')
    if len(cpf) == 9: #se está ok não precisa mais continuar o laço
        break
    #possivelmente mais código aqui

See running on ideone . And No Coding Ground . Also put it on GitHub for future reference .

Essentially in console applications this is how it is done. Of course you have to abstract so you do not get repetitive. There are other techniques for joining together.

To restart your application you can create the following method:

import sys
import os
def restart_program():
    python = sys.executable
    os.execl(python, python, * sys.argv)

Then when you want to restart the application you call:

restart_program()

More depending on the problem you can do a simple loop repetition for example:

while True:
    cpf = input('Digite os nove primeiros dígitos do CPF: ')
    if len(cpf) == 9:
        break
    else:
        continue

I think in your case working with the loop would be the best option

Actually, the comment above is correct, but if it is something to just call the option to enter the CPF again, you can use the repetition (as in the comment above):

cpf = input('Digite os nove primeiros dígitos do CPF: ')
if len(cpf) != 9:
     break
     #Para a operação
else:
     continue