writes transparency as rgba to ~/.Xresources

def write_transparency(selection):
    """writes transparency as rgba to ~/.Xresources"""
    global themefile, transparency, prefix

    if themefile == "":
        return

    lines = themefile.split('\n')

    for line in lines:
        if 'background' in line.lower():
            try:
                background = line.split(':')[1].replace(' ', '')
                background = background.replace('\t', '')
                break
            except:
                msg = ('Cannot determine background color from themefile. '
                       'Defaulting to: #000000')
                print msg
                background = '#000000'
                break
        else:
            background = '#000000'

    background = hex_to_rgb(background)

    fd, tmpfile = tempfile.mkstemp()
    if exists( XRESOURCES ):
        old = open( XRESOURCES )
        new = os.fdopen(fd, 'w')
        for line in old:
            lline = line.lower()

            if 'depth' in lline:
                continue

            elif 'rgba' in lline:
                continue

            elif line == '\n':
                continue

            else:
                os.write(fd, line)

        os.write(fd, '\n%s.depth:\t32' % prefix)
        os.write(fd, '\n%s.background:\trgba:%s/%s\n' %
                 (prefix, background, decimal_to_alpha(transparency)))
        old.close()
        new.close()
        move( tmpfile, XRESOURCES )