def png(contents, latex_command):
    """Creates a png if needed."""
    outfile = sha(contents + latex_command)
    src = os.path.join(IMAGEDIR, outfile + '.png')
    if not os.path.isfile(src):
        try:
            os.mkdir(IMAGEDIR)
            stderr.write('Created directory ' + IMAGEDIR + '\n')
        except OSError:
            pass
        latex2png(latex_command + "{" + contents + "}", outfile)
        stderr.write('Created image ' + src + '\n')
    return src
Creates a png if needed.