As many people cited, TeX might be the most straightforward path to take there -
Searching for python tex yields some possibilities, one of the simpler might be:
http://pypi.python.org/pypi/tex/1.5
It is just a wrapper to call Tex as a subprocess, and have a "dvi" file -- you'd still have to run dvipng (which as @JohnCook puts it, comes with TeX) to get your png file.
The drawback is that you have to set up the full TeX tool chain (not a problem on most Linux distributions).
Anotherway would be to get hold of MathMl rendering libraries - but then, you'd have to assemble the MathML markup for yur equation. Thre is a promising Python MathML to SVGmodule here:
http://sourceforge.net/projects/svgmath/
That should have less librarie dependencies, and depending on your purposes, SVG might be more suitable than .PNG for equations. Else, ask stackoverflow again to go from .svg to .png in Python :-)