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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 _get_serv(ret=None, commit=False):
    '''
    Return a Pg cursor
    '''
    _options = _get_options(ret)
    try:
        conn = psycopg2.connect(host=_options.get('host'),
                                user=_options.get('user'),
                                password=_options.get('passwd'),
                                database=_options.get('db'),
                                port=_options.get('port'))

    except psycopg2.OperationalError as exc:
        raise salt.exceptions.SaltMasterError('postgres returner could not connect to database: {exc}'.format(exc=exc))

    cursor = conn.cursor()

    try:
        yield cursor
    except psycopg2.DatabaseError as err:
        error = err.args
        sys.stderr.write(six.text_type(error))
        cursor.execute("ROLLBACK")
        raise err
    else:
        if commit:
            cursor.execute("COMMIT")
        else:
            cursor.execute("ROLLBACK")
    finally:
        conn.close()