a thread-local, context-preserving Python logger
Project description
log-with-context is a Python logger that saves variables in a thread-local context to be passed as extra to Python logging methods.
Note that log-with-context assumes that you are passing context in a multithreading sense–not in an asyncio sense.
Installation
This library is available on PyPI and can be installed with
python3 -m pip install log-with-context
Usage
This library provides a wrapped Python logging.Logger that adds a shared context to each logging message, passed as the extra parameter.
You will need an additional library (like JSON-log-formatter) to actually output the logging messages. We avoided putting this functionality in this library to keep it lightweight and flexible. We assumed that you already have a preferred way to format your logging messages.
import logging
import logging.config
from log_with_context import add_logging_context, Logger
logging.config.dictConfig({
"version": 1,
"disable_existing_loggers": True,
"formatters": {
"json": {"()": "json_log_formatter.JSONFormatter"},
},
"handlers": {
"console": {
"formatter": "json",
"class": "logging.StreamHandler",
}
},
"loggers": {
"": {"handlers": ["console"], "level": "INFO"},
},
})
LOGGER = Logger(__name__)
LOGGER.info("First message. No context")
with add_logging_context(current_request="hi"):
LOGGER.info("Level 1")
with add_logging_context(more_info="this"):
LOGGER.warning("Level 2")
LOGGER.info("Back to level 1")
LOGGER.error("No context at all...")
The above program logs the following messages to standard error:
{"message": "First message. No context", "time": "2021-04-08T16:37:23.126099"}
{"current_request": "hi", "message": "Level 1", "time": "2021-04-08T16:37:23.126336"}
{"current_request": "hi", "more_info": "this", "message": "Level 2", "time": "2021-04-08T16:37:23.126389"}
{"current_request": "hi", "message": "Back to level 1", "time": "2021-04-08T16:37:23.126457"}
{"message": "No context at all...", "time": "2021-04-08T16:37:23.126514"}
This example may look trivial, but it is very handy to maintain a logging context up and down a Python call stack without having to pass additional variables to the functions and methods that you call.
Implementation details
Logging contexts are stored as thread-local variables. If you want to share information between threads, you must create a Logging context in each thread with the same information.
Similarly, logging contexts are deliberately not copied when creating subprocesses. This is done to minimize bugs and make sure that log-with-context behaves in the exact same manner across operating systems.
Project details
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