my_figure.py

import pylab 
import numpy 
import os

# Make a simple plot
x = numpy.arange(1, 100, 1)
y = x**2
pylab.plot(x, y)

# Define a filename (remember the .pdf)
filename = "my_file.pdf"

# Save and convert!
pylab.savefig(filename)
os.system("pdfcrop %s %s" % (filename, filename))