def replace_simple_tags(string, from_tag="italic", to_tag="i", to_open_tag=None):
    """
    Replace tags such as <italic> to <i>
    This does not validate markup
    """
    if to_open_tag:
        string = string.replace("<" + from_tag + ">", to_open_tag)
    elif to_tag:
        string = string.replace("<" + from_tag + ">", "<" + to_tag + ">")
        string = string.replace("<" + from_tag + "/>", "<" + to_tag + "/>")
    else:
        string = string.replace("<" + from_tag + ">", "")
        string = string.replace("<" + from_tag + "/>", "")

    if to_tag:
        string = string.replace("</" + from_tag + ">", "</" + to_tag + ">")
    else:
        string = string.replace("</" + from_tag + ">", "")

    return string