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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 rewrite_links(self, func):
 """ Add a callback for rewriting links. The callback should take a single argument, the url, and should return a replacement url. The callback function is called everytime a ``[]()`` or ``<link>`` is processed. You can use this method as a decorator on the function you want to set as the callback. """

        @libmarkdown.e_url_callback
        def _rewrite_links_func(string, size, context):
            ret = func(string[:size])
            if ret is not None:
                buf = ctypes.create_string_buffer(ret)
                self._alloc.append(buf)
                return ctypes.addressof(buf)

        self._rewrite_links_func = _rewrite_links_func
        return func