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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 list_milestones(self, project_id, find=None):
 """ This lets you query the list of milestones for a project. You can either return all milestones, or only those that are late, completed, or upcoming. """

        path = '/projects/%u/milestones/list' % project_id
        req = ET.Element('request')
        if find is not None:
            ET.SubElement(req, 'find').text = str(find)
        return self._request(path, req)