Hello all! I wanted to introduce a small discussion concerning logging / formatting. Python formatting is one of those things that does not follow its own Python Zen `There should be one-- and preferably only one --obvious way to do it`… We have had

%

-interpolation,

.format

and f-strings. I personally avoid

%

-interpolation;

.format

is very popular but I almost always use f-strings. The

logging

module is the sole exception, in my opinion, where

%

-interpolation should be used, because it uses lazy evaluation:

logger.debug('My object is %s', some_object)

In that example, the

some_object.__str__

method will not be called if the logger level (or is it the handler?) is not low enough to process debug messages. This is different from

logger.debug('My object is %s'%my_object)

or

logger.debug('My object is {}'.format(my_object))

or

logger.debug(f'My object is {my_object}')

because of lazy evaluation: the string will be formatted, then sent to the logger. In a Prefect server setting, where logs are sent to the server, each log record needs to be serializable. This is achieved with

json.dumps

on the

record

received by

prefect.utilities.logging.CloudHandler.emit

This

record

has a field

args

with the args passed to the

logger.log

call, which can have non-serializable objects. What I have seen is that the server logs have many critical messages saying:

Failed to write log with error: TypeError: Object of type X is not JSON serializable

I can change my logging calls to do

logging.debug('My object is %s', str(my_object))

but I really feel like this is a workaround for a bug in

CloudHandler

: perhaps the

args

should not be sent to the server, or unserializable args objects could be redacted. What do you guys think is the appropriate fix here?

Hi @David Ojeda - good news, I think the solution is already PR’d and will be available shortly: https://github.com/PrefectHQ/prefect/pull/2444

Cool! Great news as usual!