xs = [1, 2, 3, 4, 5, 6, 7, 8, 9]

def f(x):
    return (x-5.2)*(x-5.2)

print(min(xs))			# min(1,2,3,4,5,6,7,8,9)
print(min(xs, key=f))		# min(f(1), f(2), ....) !!!