import matplotlib.patches as patches
import matplotlib.pyplot as plt
fig, axs = plt.subplots(1,1)
t1 = axs.text(0.4,0.6, 'Hello world line 1', ha='center', color='red', weight='bold', transform=axs.transAxes)
t2 = axs.text(0.5,0.5, 'Hello world line 2', ha='center', color='green', weight='bold', transform=axs.transAxes)
t3 = axs.text(0.6,0.4, 'Hello world line 3', ha='center', color='blue', weight='bold', transform=axs.transAxes)
fig.canvas.draw()
textobjs = [t1,t2,t3]
xmin = min([t.get_window_extent().xmin for t in textobjs])
xmax = max([t.get_window_extent().xmax for t in textobjs])
ymin = min([t.get_window_extent().ymin for t in textobjs])
ymax = max([t.get_window_extent().ymax for t in textobjs])
xmin, ymin = fig.transFigure.inverted().transform((xmin, ymin))
xmax, ymax = fig.transFigure.inverted().transform((xmax, ymax))
rect = patches.Rectangle((xmin,ymin),xmax-xmin,ymax-ymin, facecolor='grey', alpha=0.2, transform=fig.transFigure)
axs.add_patch(rect)