### Exercice 21
def g(liste):
    return liste[0 : len(liste)]

### Exercice 22
grille = [ [0] * 3 for i in range(3) ]
copie = grille.copy()
copie[0] = [1, 2, 3]
copie[1][0] = 4

### Exercice 23
from copy import deepcopy

grille = [ [0] * 3 for i in range(3) ]
copie = deepcopy(grille)