Encrypt some fields in log messages

tpl.py

import logging
import logging.config

# pip install cryptography
from cryptography.fernet import Fernet

# FROM https://github.com/madzak/python-json-logger/blob/master/src/pythonjsonlogger/jsonlogger.py#L18
RESERVED_ATTRS = ('args', 'asctime', 'created', 'exc_info', 'exc_text',
                  'filename', 'funcName', 'levelname', 'levelno', 'lineno',
                  'module', 'msecs', 'message', 'msg', 'name', 'pathname',
                  'process', 'processName', 'relativeCreated', 'stack_info',
                  'thread', 'threadName')

SECRET_KEYS = {'sid', 'password', 'username'}


def merge_record_extra(record, target, reserved):
    """
    Merges extra attributes from LogRecord object into target dictionary
    :param record: logging.LogRecord
    :param target: dict to update
    :param reserved: dict or list with reserved keys to skip
    """
    for key, value in record.__dict__.items():
        # this allows to have numeric keys
        if (key not in reserved
                and not (hasattr(key, "startswith") and key.startswith('_'))):
            target[key] = value
    return target


key = b'7Kpw9lLjN3BEBqz-hMPURwKIKX-aP-Q2VZUVnD8PyDw='
fernet = Fernet(key)
token = fernet.encrypt(b"A really secret message. Not for prying eyes.")


class FormatterWithExtra(logging.Formatter):
    def format(self, record):
        extras = merge_record_extra(
            record=record,
            target=dict(),
            reserved=RESERVED_ATTRS,
        )
        record.extras = ', '.join('{}={}'.format(
            k,
            fernet.encrypt(v.encode()) if k in SECRET_KEYS else v)
                                  for k, v in extras.items())
        return super().format(record)


config = {
    'version': 1,
    'disable_existing_loggers': False,
    'formatters': {
        'standard': {
            'class': '__main__.FormatterWithExtra',
            'format': '%(levelname)s %(message)s %(extras)s',
        },
    },
    'handlers': {
        'standard': {
            'class': 'logging.StreamHandler',
            'formatter': 'standard',
        },
    },
    'loggers': {
        '': {
            'handlers': ['standard'],
            'level': logging.INFO,
        },
    },
}
logging.config.dictConfig(config)

logger = logging.getLogger(__name__)

logger.warning('test', extra={'a': 1, 'sid': 'this is secret'})

# For generating a new KEY
# KEY = Fernet.generate_key()
# print(KEY)

# For decrypting
# key = b'7Kpw9lLjN3BEBqz-hMPURwKIKX-aP-Q2VZUVnD8PyDw='
# fernet = Fernet(key)
# string = fernet.decrypt(token).decode()

This code returns:

WARNING test a=1, sid=b'gAAAAABgjUbrVcO3nxGhQoa2dEYe3aZOrGIee7T3l8ST95fPX7UxNLR61TQKRBQvkBScZx7Y_nHROE8JsBlphY4fMnfOYMDU7g=='