Adding caption below X-axis for a scatter plot using matplotlib

Question

I am pretty new to python and to the matplotlib library. I have created a scatter plot using matplotlib and now I wish to add caption a little below the X-axis. This is my code:

Answer 1

First, I feel weird posting an answer against the co-lead developer of matplotlib. Obviously, @tacaswell knows matplotlib far better than I ever will. But at the same time, his answer wasn't dynamic enough for me. I needed a caption that would always be based on the position of the xlabel, and couldn't just use text annotations.

I considered simply changing the xlabel to add a newline and the caption text, but that wouldn't clearly differentiate the caption, and you can't do things like change the text size or make it italic in the middle of a text string.

I solved this by using matplotlib's TeX capabilities. Here's my solution:

from matplotlib import pyplot as plt
from matplotlib import rc
import numpy as np
from pylab import *

rc('text', usetex=True)

file = open('distribution.txt', 'r')

txt="I need the caption to be present a little below X-axis"

x=[]
y=[]
for line in file:
    new=line.rstrip()
    mystring=new.split("\t")
    x.append(mystring[0])
    y.append(mystring[1])


fig = plt.figure()
ax1 = fig.add_axes((0.1,0.4,0.8,0.5))
ax1.set_title("This is my title")
ax1.set_xlabel(r'\begin{center}X-axis\\*\textit{\small{' + txt + r'}}\end{center}')
ax1.set_ylabel('Y-axis')
ax1.scatter(x,y, c='r')
plt.xlim(0, 1.05)
plt.ylim(0, 2.5)
plt.show()

I did the same thing with the random scatter plot from tacaswell's answer, and here's my result:

One warning: if you tweak this to take input string variables, the strings may not be properly escaped for use with TeX. Escaping LaTeX code is already covered on Stack Overflow, at https://stackoverflow.com/a/25875504/1404311 . I used that directly, and then could take arbitrary xlabels and captions.