Lazy log message formatting

[TheJJ]

Our logging system does not support lazy message formatting, like the python logging module.

from log import info

# current version: always performs string formatting
var = "with formatting"
info("some message %s" % var)

# new version: should only format the string if the message is actually emitted
var = "lazyness"
info("everything is better™ with ", var)

The functions are in openage/log/__init__.py and then relay the messages to libopenage.
The formatting of messages should thus happen (either in C++ or the python part, not sure) only if the log level of the message is higher than the minimum log level of a sink that gets the message.

Possible approach:

• Use the python standard logging module so it logs to our C++ as backend
• Notify the logging module about log levels from C++
• Let all the magic be done by the standard logging module then, our functions can be aliases, or we just only use logging all over the python codebase.

This is an optimization, so no real priority 😉

[kev946]

Are we just trying to do lazy formatting on the messages sent from the Python side?

[TheJJ]

We can do both, in C++ and Python. The C++ operator << could be abused for that, and we would have to store references to the message parts, to merge them later if the message has to be formatted.

We could add that C++ (which controls the loglevel) notifies Python of the current level, so messages are not even transported C++ if the message is not important enough.

[TheJJ]

I added a possible approach section above, with the main idea to create a backend for our C++ logger for the python logging module.

[kev946]

For the Python side, maybe we could create a CppHandler class derived from Handler. We override setLevel and emit to call into the C++ side. Does this sound good?

[TheJJ]

Yes, except that we have to call setLevel from the C++ side so the C++-level is set in the python world.

[TheJJ]

C++ side was done in #1029.

[TheJJ]

Python side in #1025.

[TheJJ]

🎉