Pass log kwargs to custom sink

[volfco]

Loguru supports string formatting, but it seems that these kwargs are dropped if there is nothing to format in the string. I would think these would be passed to the custom sink, but it does not seem like this is the case.

See the below example.

>>> from loguru import logger
>>> 
>>> def callback(payload):
...     print(payload)
... 
>>> logger.start(callback, serialize=True)
>>> logger.info("testing", hello="world")
2018-12-08 15:56:07.675 | INFO     | __main__:<module>:1 - yoo
{"text": "2018-12-08 15:56:07.675 | INFO     | __main__:<module>:1 - testing\n", "record": {"elapsed": {"repr": "0:01:35.065585", "seconds": 95.065585}, "exception": null, "extra": {}, "file": {"name": "<stdin>", "path": "<stdin>"}, "function": "<module>", "level": {"icon": "\u2139\ufe0f", "name": "INFO", "no": 20}, "line": 1, "message": "testing", "module": "<stdin>", "name": "__main__", "process": {"id": 22013, "name": "MainProcess"}, "thread": {"id": 140289032955392, "name": "MainThread"}, "time": {"repr": "2018-12-08 15:56:07.675593-06:00", "timestamp": 1544306167.675593}}}
>>> logger.info("testing {hello}", hello="world")
2018-12-08 15:58:37.702 | INFO     | __main__:<module>:1 - testing world
{"text": "2018-12-08 15:58:37.702 | INFO     | __main__:<module>:1 - testing world\n", "record": {"elapsed": {"repr": "0:04:05.092374", "seconds": 245.092374}, "exception": null, "extra": {}, "file": {"name": "<stdin>", "path": "<stdin>"}, "function": "<module>", "level": {"icon": "\u2139\ufe0f", "name": "INFO", "no": 20}, "line": 1, "message": "testing world", "module": "<stdin>", "name": "__main__", "process": {"id": 22013, "name": "MainProcess"}, "thread": {"id": 140289032955392, "name": "MainThread"}, "time": {"repr": "2018-12-08 15:58:37.702382-06:00", "timestamp": 1544306317.702382}}}

I would expect that {"hello": "world"} to be somewhere in the payload passed to the custom sink

[volfco]

Reading a bit more it looks like you can use logger.bind().info, but that seems like an unnecessary extra step.

[Delgan]

Hey, thanks for your interest and suggestion!

So, you are looking for a behavior similar to the one of the structlog, right?

I thought about it, unfortunately I do not think it's possible.
log(msg, *args, **kwargs) is just a convenient shorthand for log(msg.format(*args, **kwargs)), adding special case and condition would break this simplicity rule.
But then, there is also a implementation issue. What should I do in the case of log("{a}", a=1, b=2)? There is no way to know that only a has been formatted and that only b should be passed somewhere else.

I agree that structlog is probably more suitable for this use-case. I can't think of a way to conveniently mix message formatting and structuring. :/

logger.bind(hello="world").info("Message") is the way Loguru has been build to deal with in-line binding of extra data. Is it too verbose?

[volfco]

I didn't know structlog existed. Neat. I guess- yes.

I don't see why it matters if the data is used by .format or not? If I'm consuming the data in an output function, I should be aware that the message might already be formatted.

[Delgan]

@volfco I am closing this issue as I can't find a solution that would fit in the api as I would like.

I prefer to avoid special cases and I try to stay close to the "one way of do it" principle. Structured logging in Loguru is performed using .bind(). Using .log(msg, *arg, **kwgars) is just a shorthand for .log(msg.format(*args, **kwargs)), nothing more.

A basic example:

logger.start(sys.stderr, format="[{time}][{level}] {message} | {extra}")

app, version = "MyApp", "0.2.3"
ip, port = "192.168.0.10", 22

logger.info("Starting '{}' (v{})", app, version)
logger.bind(ip=ip, port=port).info("Sending a request")

For advanced structured logging, Loguru can't beat structlog anyway, which is a very well polished library.

[Delgan]

Well, I'm sorry it took a year and a half, but... This feature is finally available. 🙂

The **kwargs arguments are automatically added to the extra dict. This can be disabled using .opt(capture=False).

[volfco]

🥳