plt.figure ルーチン全体は次のようになります。
fig = plt.figure()
axplot_topleft = fig.add_subplot(2,2,1)
axplot_topleft.xaxis.set_major_formatter(nullfmt)
axplot_topleft.set_yticks([-8, -6, -4, -2, 0, 2, 4, 6])
axplot_topright = fig.add_subplot(2,2,2)
axplot_topright.xaxis.set_major_formatter(nullfmt)
axplot_topright.yaxis.set_major_formatter(nullfmt)
axplot_bottomleft = fig.add_subplot(2,2,3)
axplot_bottomleft.set_xticks([0, 1, 2, 3, 4 ,5 ,6])
axplot_bottomleft.set_yticks([-8, -6, -4, -2, 0, 2, 4, 6])
axplot_bottomright = fig.add_subplot(2,2,4)
axplot_bottomright.yaxis.set_major_formatter(nullfmt)
axplot_bottomright.set_xticks([0, 1, 2, 3, 4 ,5 ,6])