emptylog 0.0.4

Mimicking the logger protocol

emptylog: some tools for logging

This package ensures compatibility of any logger implementations with the built-in logging library.

Table of contents

• Installing
• Universal Logger Protocol
• Empty Logger
• Memory Logger

Installing

Install it from Pypi:

pip install emptylog

You can also quickly try out this and other packages without having to install using instld.

Universal Logger Protocol

Easily check whether an object is a logger using the protocol. The protocol contains 6 classic logger methods:

def debug(message: str, *args: Any, **kwargs: Any) -> None: pass
def info(message: str, *args: Any, **kwargs: Any) -> None: pass
def warning(message: str, *args: Any, **kwargs: Any) -> None: pass
def error(message: str, *args: Any, **kwargs: Any) -> None: pass
def exception(message: str, *args: Any, **kwargs: Any) -> None: pass
def critical(message: str, *args: Any, **kwargs: Any) -> None: pass

The protocol is verifiable in runtime by the isinstance function. Let's check this on a regular logger from logging:

import logging
from emptylog import LoggerProtocol

print(isinstance(logging.getLogger('some_name'), LoggerProtocol))  # True

This also works for third-party loggers with the same signature. Let's try it on loguru:

from loguru import logger
from emptylog import LoggerProtocol

print(isinstance(logger, LoggerProtocol))  # True

And of course, you can use the protocol for type hints:

def function(logger: LoggerProtocol):
    logger.info('There was an earthquake in Japan, check the prices of hard drives!')

The protocol can be used for static checks by any tool you prefer, such as mypy.

Empty Logger

EmptyLogger is the simplest implementation of the logger protocol. When calling logging methods from an object of this class, nothing happens. You can use it as a stub, for example, when defining functions:

from emptylog import EmptyLogger, LoggerProtocol

def function(logger: LoggerProtocol = EmptyLogger()):
    logger.error('Kittens have spilled milk, you need to pour more.')

Memory Logger

MemoryLogger is a special class designed for tests. Its difference from EmptyLogger is that it remembers all the times it was called.

The call history is stored in the data attribute and sorted by logger method names:

from emptylog import MemoryLogger

logger = MemoryLogger()

logger.error('Joe Biden forgot his name again.')
logger.error('And again.')
logger.info("Joe, remember, you're Joe.")

print(logger.data)
# LoggerAccumulatedData(debug=[], info=[LoggerCallData(message="Joe, remember, you're Joe.", args=(), kwargs={})], warning=[], error=[LoggerCallData(message='Joe Biden forgot his name again.', args=(), kwargs={}), LoggerCallData(message='And again.', args=(), kwargs={})], exception=[], critical=[])

print(logger.data.info[0].message)
# Joe, remember, you're Joe.
print(logger.data.error[0].message)
# Joe Biden forgot his name again.
print(logger.data.info[0].args)
# ()
print(logger.data.info[0].kwargs)
# {}

You can find out the total number of logs saved by MemoryLogger by applying the len() function to the data attribute:

logger = MemoryLogger()

logger.warning("Are you ready, kids?")
logger.info("Aye, aye, Captain!")
logger.error("I can't hear you!")
logger.info("Aye, aye, Captain!")
logger.debug("Oh!")

print(len(logger.data))
# 5