Enabling @debug · helpdesk (published)

Stream: helpdesk (published)

Topic: Enabling @debug

mbaz (May 26 2021 at 22:37):

How can I enable/disable printing of @debug?
Apparently I need to set JULIA_DEBUG, but I can't find what to set it to.

Update: I think I got it; it's set to the module name where debug messages are activated.

Andrey Oskin (May 27 2021 at 05:30):

You can also use global_logger

Andrey Oskin (May 27 2021 at 05:31):

Just create logger with the needed level and make it active with global_logger command

mbaz (May 27 2021 at 13:14):

The documentation on logging badly needs an example or two. I find it impossible to understand.

Fredrik Ekre (May 27 2021 at 13:16):

using Logging

# Create logger with Debug level printing to stderr
debuglogger = ConsoleLogger(stderr, Logging.Debug)

# Set this logger as the global logger
global_logger(debuglogger)

Thanks! I kind of see how it works, but:
1) Logging.Debug is not in the docs as far as I can see
2) What does it mean for a logger to be "global"? If I run this in my module, will it enable debug messages in other modules?
3) How do I turn it off? Do I need to create a NullLogger and set it as global?
4) Will debuglogger ignore @info messages?

Fredrik Ekre (May 27 2021 at 13:28):

Please contribute!
Global to that Julia session. This is inherited by all tasks. To use a logger locally you can use e.g.

with_logger(debuglogger) do
      # do stuff
end

The default logger is ConsoleLogger(stderr, Logging.Info) (the current logger is also returned from global_logger, so the code above could be oldlogger = global_logger(debuglogger) and then global_logger(oldlogger) to return to the previous state.
No, the level you give is the minimal level, so anything above Logging.Debug will go through.

Fredrik Ekre (May 27 2021 at 13:29):

I recommend having a look at LoggingExtras.jl, in particular the README which includes a lot of useful information.

Andrey Oskin (May 27 2021 at 13:30):

https://docs.julialang.org/en/v1/stdlib/Logging/#Log-event-structure

But it can be better, probably.

Andrey Oskin (May 27 2021 at 13:31):

I mean, it is written "There are several standard levels of type LogLevel; user-defined levels are also possible. Each is distinct in purpose:" and key words after that.

But maybe it would be better to write Logging.Debug instead of just Debug, since it is not exported anyway.

Fredrik Ekre (May 27 2021 at 13:32):

The standard log levels could have their own docstrings, which would help in search I bet.

mbaz (May 27 2021 at 13:38):

If I can figure this stuff out, I'll certainly contribute to the docs. I'll also take a look at LoggingExtras.
More questions:
1) The default logger has level Logging.Info, but only @debug is ignored; @info, @warn and @error all produce messages. How does this work?
2) I have a large module with @debug scattered around. There may even be @debugs, @infos and @warns in the same function/block of code. How do I turn @debug on/off without affecting the others? I can do this with JULIA_DEBUG, so it must be possible, but I don't see how to do it with the Logging module functions.

Fredrik Ekre (May 27 2021 at 13:44):

Because the level is the minum: info, warn, and error levels are all larger or equal to that level so the messages are displayed

Fredrik Ekre (May 27 2021 at 13:45):

You can not really do that with the Logging stdlib only so you need LoggingExtras.jl. There is an example in the README for filtering out everything from HTTP.jl (https://github.com/oxinabox/LoggingExtras.jl#filterout-any-messages-from-http)

mbaz (May 27 2021 at 13:46):

Andrey Oskin said:

I mean, it is written "There are several standard levels of type LogLevel; user-defined levels are also possible. Each is distinct in purpose:" and key words after that.

But maybe it would be better to write Logging.Debug instead of just Debug, since it is not exported anyway.

Maybe it's just me, but I feel like the docs could be more explicit, or simply show a couple of examples to clarify. It was not obvious to me that Debug is meant to be used as Logging.Debug and that it corresponds to a number. The docs also imply that the level are ordered, but the order is not made explicit (although it makes sense to assume it is Info<Debug<Warn<Error).