Python - getting back to the line with input

Question

I don't know how to go back to a line in python, how do I do that?

filesize = input("Podaj rozmiar pliku i jednostke (np. \"100 mb\", \"130 gb\", \"84 kb\"): ")

if filesize[-3:] ==  ' mb' or filesize[-3:] == ' kb' or filesize[-3:] == ' gb':
    print("true")
else:
    print("Podaj jeszcze raz rozmiar pliku w formacie [liczba format] np. 12 kb")
    #AND HERE I WANT TO TAKE IT BACK UP TO filesize BECAUSE ITS AN ERROR MSG

Answer 1

An easy way to do this is with a while loop and a flag. This will run the first time and will continue to ask for input until valid input is given, at which point it will continue.

badInput = True
while badInput:
    filesize = input("Podaj rozmiar pliku i jednostke (np. \"100 mb\", \"130 gb\", \"84 kb\"): ")
    if filesize[-3:] ==  ' mb' or filesize[-3:] == ' kb' or filesize[-3:] == ' gb':
        badInput = False
        print("true")
    else:
        print("Podaj jeszcze raz rozmiar pliku w formacie [liczba format] np. 12 kb")