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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 pk_field(self):
        '''
        Name of the primary key field as retrieved from rethinkdb table
        metadata, 'id' by default. Should not be overridden. Override
        `table_create` if you want to use a nonstandard field as the primary
        key.
        '''
        if not self._pk:
            try:
                pk = self.rr.db('rethinkdb').table('table_config').filter({
                    'db': self.rr.dbname, 'name': self.table}).get_field(
                            'primary_key')[0].run()
                self._pk = pk
            except Exception as e:
                raise Exception(
                        'problem determining primary key for table %s.%s: %s',
                        self.rr.dbname, self.table, e)
        return self._pk