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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 _process_dbxref(self):
 """ We bring in the dbxref identifiers and store them in a hashmap for lookup in other functions. Note that some dbxrefs aren't mapped to identifiers. For example, 5004018 is mapped to a string, In those cases, there just isn't a dbxref that's used when referencing with a cvterm; it'll just use the internal key. :return: """


        raw = '/'.join((self.rawdir, 'dbxref'))
        LOG.info("processing dbxrefs")
        line_counter = 0

        with open(raw, 'r') as f:
            filereader = csv.reader(f, delimiter='\t', quotechar='\"')
            f.readline()  # read the header row; skip
            for line in filereader:
                (dbxref_id, db_id, accession, version, description, url) = line
                # dbxref_id	db_id	accession	version	description	url
                # 1	2	SO:0000000	""

                accession = accession.strip()
                db_id = db_id.strip()
                if accession != '' and db_id in self.localtt:
                    # scrub some identifiers here
                    mch = re.match(
                        r'(doi|SO|GO|FBcv|FBbt_root|FBdv|FBgn|FBdv_root|FlyBase|FBbt):',
                        accession)
                    if mch:
                        accession = re.sub(mch.group(1)+r'\:', '', accession)
                    elif re.match(
                            r'(FlyBase miscellaneous CV|cell_lineprop|relationship type|FBgn$)',
                            accession):
                        continue
                    elif re.match(r'\:', accession):  # starts with a colon
                        accession = re.sub(r'\:', '', accession)
                    elif re.search(r'\s', accession):
                        # skip anything with a space
                        # LOG.debug(
                        #   'dbxref %s accession has a space: %s', dbxref_id, accession)
                        continue

                    if re.match(r'http', accession):
                        did = accession
                    else:
                        prefix = self.localtt[db_id]
                        did = ':'.join((prefix, accession))
                        if re.search(r'\:', accession) and prefix != 'DOI':
                            LOG.warning('id %s may be malformed; skipping', did)

                    self.dbxrefs[dbxref_id] = {db_id: did}

                elif url != '':
                    self.dbxrefs[dbxref_id] = {db_id: url.strip()}
                else:
                    continue

                # the following are some special cases that we scrub
                if int(db_id) == 2 and accession.strip() == 'transgenic_transposon':
                    # transgenic_transposable_element
                    self.dbxrefs[dbxref_id] = {
                        db_id: self.globaltt['transgenic_transposable_element']}

                line_counter += 1

        return