How to access an object outside of a multiprocessing process?

here is my code

from multiprocessing import Pool
a = []
def f(x):
    a.append(x*x)
    return x*x

if __name__ == '__main__':
    with Pool(5) as p:
        print(p.map(f, [1, 2, 3]))


print(a)

I would expect print(a) to output [1,4,9]. However, it just outputs an empty array. Is there a way to easily fix this, ideally allowing f() to access a?