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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _build_url(cls, request, path=None, **changes):
 """Builds a response URL by overriding the original queries with specified change queries. Change queries set to None will not be used. Setting a change query to False will remove it even if there is an original query with a value. """

        changes = {k: v for k, v in changes.items() if v is not None}
        queries = {**request.url.query, **changes}
        queries = {k: v for k, v in queries.items() if v is not False}
        query_strings = []

        def add_query(key):
            query_strings.append('{}={}'.format(key, queries[key])
                                 if queries[key] != '' else key)

        def del_query(key):
            queries.pop(key, None)

        if 'head' in queries:
            add_query('head')
            del_query('head')

        if 'start' in changes:
            add_query('start')
        elif 'start' in queries:
            add_query('start')

        del_query('start')

        if 'limit' in queries:
            add_query('limit')
            del_query('limit')

        for key in sorted(queries):
            add_query(key)

        scheme = cls._get_forwarded(request, 'proto') or request.url.scheme
        host = cls._get_forwarded(request, 'host') or request.host
        forwarded_path = cls._get_forwarded(request, 'path')
        path = path if path is not None else request.path
        query = '?' + '&'.join(query_strings) if query_strings else ''

        url = '{}://{}{}{}{}'.format(scheme, host, forwarded_path, path, query)
        return url