Rutina para añadir parámetros a una URL

from urlparse import urlparse, urlunparse
from urllib import urlencode

def parametrize_url(url, **params):
    """ don't just add the **params because the url
    itself might contain CGI variables embedded inside
    the string. """
    url_parsed = list(urlparse(url))

    encoded = urlencode(params)
    qs = url_parsed[4]
    if encoded:
        if qs:
            qs += '&'+encoded
        else:
            qs = encoded
    netloc = url_parsed[1]
    if netloc.find('?')>-1:
        url_parsed[1] = url_parsed[1][:netloc.find('?')]
        if qs:
            qs = netloc[netloc.find('?')+1:]+'&'+qs
        else:
            qs = netloc[netloc.find('?')+1:]

    url_parsed[4] = qs

    url = urlunparse(url_parsed)
    return url