pl.pie([i, 2], labels=['a', 'b'], autopct='%1.1f%%')
fig = pl.gcf()
axe = fig.add_axes([0.4, 0.4, 0.2, 0.2])
pie = pl.pie([1, 1], labels=['a', 'b'])
l = pl.legend(title='sample', loc='center')
for group in pie:
    for x in group:
        x.set_visible(False)
pl.show()
matplotlib - Legend in separate subplot