Middleware to move tags <script> to the bottom

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import re


FIND_SCRIPT_TAGS = re.compile(r'(<script .*?>.*?</script>)', re.DOTALL)

class ScriptsAtBottomMiddleware(object):
    """Finds all tags <script> at the HTML response and move to the end of the document,
    before tag </html>.
    
    This makes the page load faster, because <script> blocks parallel loading.
    
    Read more about this at:
        - http://developer.yahoo.com/performance/rules.html#js_bottom
        - http://code.google.com/intl/pt-BR/speed/page-speed/docs/rtt.html#PutStylesBeforeScripts
    """

    def process_response(self, request, response):
        if response['content-type'][:9] == 'text/html':
            # Find scripts tags with src
            f = FIND_SCRIPT_TAGS.findall(response.content)
            
            # Remove the tags found
            for tag in f: response.content = response.content.replace(tag, '')
            
            # Insert the tags found at the bottom
            pos = response.content.find('</html>')
            response.content = response.content[:pos] + '\n'.join(f) + '\n' + response.content[pos:]

        return response

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Comments

springlo (on November 4, 2010):

我要拜你为师。

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pkoch (on March 13, 2012):

Careful! You're making various copies of the response's content string! I think you might be trading server performance for client performance.

Wouldn't it be simples/more efficient to have a delayed script tag?

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