resize an image to basewidth

def resize(fname, basewidth, opFilename):
    """ resize an image to basewidth """
    if basewidth == 0:
        basewidth = 300
    img = Image.open(fname)
    wpercent = (basewidth/float(img.size[0]))
    hsize = int((float(img.size[1])*float(wpercent)))
    img = img.resize((basewidth,hsize), Image.ANTIALIAS)
    img.save(opFilename)