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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 prepare(self, hash, start, end, name, sources, sample=None):
 """ Prepare a historics query which can later be started. Uses API documented at http://dev.datasift.com/docs/api/rest-api/endpoints/historicsprepare :param hash: The hash of a CSDL create the query for :type hash: str :param start: when to start querying data from - unix timestamp :type start: int :param end: when the query should end - unix timestamp :type end: int :param name: the name of the query :type name: str :param sources: list of sources e.g. ['facebook','bitly','tumblr'] :type sources: list :param sample: percentage to sample, either 10 or 100 :type sample: int :return: dict of REST API output with headers attached :rtype: :class:`~datasift.request.DictResponse` :raises: :class:`~datasift.exceptions.HistoricSourcesRequired`, :class:`~datasift.exceptions.DataSiftApiException`, :class:`requests.exceptions.HTTPError` """

        if len(sources) == 0:
            raise HistoricSourcesRequired()
        if not isinstance(sources, list):
            sources = [sources]

        params = {'hash': hash, 'start': start, 'end': end, 'name': name, 'sources': ','.join(sources)}
        if sample:
            params['sample'] = sample
        return self.request.post('prepare', params)