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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 paths_for_download(self):
 """List of URLs available for downloading."""

        if self._paths_for_download is None:
            queries = list()
            try:
                for sra in self.gsm.relations['SRA']:
                    query = sra.split("=")[-1]
                    if 'SRX' not in query:
                        raise ValueError(
                            "Sample looks like it is not an SRA: %s" % query)
                    logger.info("Query: %s" % query)
                    queries.append(query)
            except KeyError:
                raise NoSRARelationException(
                    'No relation called SRA for %s' % self.gsm.get_accession())

            # Construction of DataFrame df with paths to download
            df = DataFrame(columns=['download_path'])
            for query in queries:
                # retrieve IDs for given SRX
                searchdata = Entrez.esearch(db='sra', term=query, usehistory='y',
                                            retmode='json')
                answer = json.loads(searchdata.read())
                ids = answer["esearchresult"]["idlist"]
                if len(ids) != 1:
                    raise ValueError(
                        "There should be one and only one ID per SRX")

                # using ID fetch the info
                number_of_trials = 10
                wait_time = 30
                for trial in range(number_of_trials):
                    try:
                        results = Entrez.efetch(db="sra", id=ids[0],
                                                rettype="runinfo",
                                                retmode="text").read()
                        break
                    except HTTPError as httperr:
                        if "502" in str(httperr):
                            logger.warn(("%s, trial %i out of %i, waiting "
                                         "for %i seconds.") % (
                                             str(httperr),
                                             trial,
                                             number_of_trials,
                                             wait_time))
                            time.sleep(wait_time)
                        elif httperr.code == 429:
                            # This means that there is too many requests
                            try:
                                header_wait_time = int(
                                    httperr.headers["Retry-After"])
                            except:
                                header_wait_time = wait_time
                            logger.warn(("%s, trial %i out of %i, waiting "
                                         "for %i seconds.") % (
                                             str(httperr),
                                             trial,
                                             number_of_trials,
                                             header_wait_time))
                            time.sleep(header_wait_time)
                        else:
                            raise httperr
                try:
                    df_tmp = DataFrame([i.split(',') for i in results.split('\n') if i != ''][1:],
                                       columns=[i.split(',') for i in results.split('\n') if i != ''][0])
                except IndexError:
                    logger.error(("SRA is empty (ID: %s, query: %s). "
                                  "Check if it is publicly available.") %
                                 (ids[0], query))
                    continue

                # check it first
                try:
                    df_tmp['download_path']
                except KeyError as e:
                    logger.error('KeyError: ' + str(e) + '\n')
                    logger.error(str(results) + '\n')

                df = concat([df, df_tmp], sort=True)
            self._paths_for_download = [path for path in df['download_path']]
        return self._paths_for_download