How do I make the width of the title box span the entire plot?

Question

consider the following pandas series s and plot

import pandas as pd
import numpy as np

s = pd.Series(np.random.lognormal(.001, .01, 100))
ax =          


        

Answer 1

Instead of scaling the bounding box of the title text itself, you can create a secondary axis above the primary one and use it as a "box" for your title. As axes normally don't look as boxes, we'll switch off its axes labels and ticks, and will set the background color to black to match the OP.

I'm using the same approach to make a secondary, matching, axis as here.

Additionally, I've used AnchoredText to snap the title text to the axis so that it can easily be located in the center of it.

import matplotlib.pyplot as plt 
from matplotlib.offsetbox import AnchoredText
from mpl_toolkits.axes_grid1 import make_axes_locatable
import pandas as pd
import numpy as np

s = pd.Series(np.random.lognormal(.001, .01, 100))
ax = s.cumprod().plot()

divider = make_axes_locatable(ax)
cax = divider.append_axes("top", size="11%", pad=0)
cax.get_xaxis().set_visible(False)
cax.get_yaxis().set_visible(False)
cax.set_facecolor('black')

at = AnchoredText("My Log Normal Example", loc=10,
                  prop=dict(backgroundcolor='black',
                            size=12, color='white'))
cax.add_artist(at)

plt.show()

Edit: for older matplotlib versions you might need to switch to cax.set_axis_bgcolor('black') when setting the background color.