def strip_tags(text, valid_tags={}):
    from BeautifulSoup import BeautifulSoup, Comment
    
    soup = BeautifulSoup(text)
    for comment in soup.findAll(text=lambda text: isinstance(text, Comment)):
        comment.extract()
    for tag in soup.findAll(True):
        if tag.name in valid_tags:
            valid_attrs = valid_tags[tag.name]
            tag.attrs = [(attr, val.replace('javascript:', '')) 
                for attr, val in tag.attrs if attr in valid_attrs]
        else:
            tag.hidden = True
    return soup.renderContents().decode('utf8')