import numpy as np
import matplotlib.pyplot as plt

plt.switch_backend('pgf')  # Switching to the PGF backend
fig, ax = plt.subplots(figsize=(6, 3.0), ncols=2, nrows=1,
                       constrained_layout=True, sharey=True)
fig.set_constrained_layout_pads(wspace=0.03)

ax[0].plot(np.arange(4), 'r', label=r'Really longgggg label 1')
ax[1].plot(np.arange(5), 'b', label=r'Really longgggg label 2')
(leg_h0, leg_lab0) = ax[0].get_legend_handles_labels()
(leg_h1, leg_lab1) = ax[1].get_legend_handles_labels()

# add a legend to one of the axes to make space at the top of the figure
leg0 = ax[0].legend(leg_h0, leg_lab0, loc='lower center',
                    bbox_to_anchor=(0.5, 1.07))

leg0.set_in_layout(True)  # force to steal space from top of the figure
# ------------------------------------------------------
# Trigger a draw (required for constrained_layout to work)
# fig.canvas.draw()   # Doesn't work since pgf is a non-interactive backend
fig.draw(fig.canvas.get_renderer())  # used to work before #15977
# ------------------------------------------------------
# Thanks constrained_layout, your work is done! turning you off now
fig.set_constrained_layout(False)

# Remove legend from axes and add a figure legend
# which includes entries from both axes
leg0.remove() 
fig_leg = fig.legend(*zip(leg_h0, leg_h1), *zip(leg_lab0, leg_lab1),
                     loc='lower center', ncol=2, columnspacing=5,
                     bbox_to_anchor=(0.5, 0.85))
fig.savefig('test.png', dpi=200)