from statistics import median, mean, quantiles, pstdev

notes = [ 2 ,4 ,5, 6 ,9 ,11 ,12, 14, 15 ,16 ,18 ]
eff =   [ 1, 3, 2 ,2 ,6 ,4, 4, 5, 3, 3, 2 ]

L = []

for i in range( len(notes) ):
    for _ in range( eff[i] ):
        L.append( notes[i] )

print( f'La médiane est: {median(L)}.' )
print( f'Les quartiles sont: {quantiles(L,n=4)}.' )
print( f'La moyenne est: {mean(L)}.' )
print( f"L'écart-type est: {pstdev(L)}." )