Pyoslog allows you to send messages to the macOS unified logging system using Python.

from pyoslog import os_log, OS_LOG_DEFAULT
os_log(OS_LOG_DEFAULT, 'Hello from Python!')

Pyoslog requires macOS 10.12 or later and Python 3.6 or later. Install using pip:

python -m pip install pyoslog

The module will install and import without error on earlier macOS versions, or on unsupported Operating Systems or incompatible Python versions. Use pyoslog.is_supported() if you need to support incompatible environments and want to know at runtime whether to use pyoslog. Please note that if is_supported() returns False then none of the module's other methods or constants will exist.

Pyoslog currently provides the following methods:

• os_log_create
• os_log_type_enabled (and info/debug variants)
• os_log_with_type
• os_log (and info/debug/error/fault variants).

All the pyoslog methods have the same signatures as their native versions, except for where a method requires a format parameter. The os_log system requires a constant (static) format specifier, and it is not possible to achieve this via Python. As a result, all instances of format strings use "%{public}s", and all messages are converted to a string before passing to the native methods.

Pyoslog also offers a helper method – log – that by default posts a message of type OS_LOG_TYPE_DEFAULT to OS_LOG_DEFAULT. For example, the shortcut log('message') is equivalent to os_log_with_type(OS_LOG_DEFAULT, OS_LOG_TYPE_DEFAULT, 'message').

The Handler class is designed for use with Python's inbuilt logging module. It works as a drop-in replacement for other Handler varieties.

See pyoslog's method documentation for a full reference.

Create a log object using os_log_create and pass it to any of the log methods to add your own subsystem and category labels:

import pyoslog
log = pyoslog.os_log_create('ac.robinson.pyoslog', 'custom-category')
pyoslog.os_log_with_type(log, pyoslog.OS_LOG_TYPE_DEBUG, 'Message to log object', log, 'of type', pyoslog.OS_LOG_TYPE_DEBUG)

Log output can be enabled or disabled globally by switching between the desired log object and pyoslog.OS_LOG_DISABLED:

import pyoslog
log = pyoslog.OS_LOG_DEFAULT
pyoslog.os_log(log, 'Log output enabled')
log = pyoslog.OS_LOG_DISABLED
pyoslog.os_log(log, 'Log output disabled')

It is also possible to check whether individual log types are enabled for a particular log object:

import pyoslog
pyoslog.os_log_type_enabled(pyoslog.OS_LOG_DEFAULT, pyoslog.OS_LOG_TYPE_DEBUG)

It is not possible to directly set a log object's mode from Python, but see the config section of man log for documentation about doing this in sudo mode.

Use the pyoslog Handler to direct messages to pyoslog:

import logging, pyoslog
logger = logging.getLogger('My app name')
logger.setLevel(logging.DEBUG)
handler = pyoslog.Handler()
handler.setSubsystem('org.example.your-app', 'filter-category')
logger.addHandler(handler)
logger.debug('message')

To configure the Handler's output type, use handler.setLevel with a level from the logging module. These are mapped internally to the OS_LOG_TYPE values – for example, handler.setLevel(logging.DEBUG) will configure the Handler to output messages of type OS_LOG_TYPE_DEBUG.

Logs can be viewed using Console.app or the log command. For example, messages sent using the default configuration can be streamed using:

log stream --predicate 'processImagePath CONTAINS [c] "python"'

Messages sent using custom log objects can be filtered more precisely. For example, to receive messages from the labelled subsystem used in the example above:

log stream --predicate 'subsystem == "ac.robinson.pyoslog"' --level debug

See man log for further details about the available options and filters.

When labelling subsystem and category using the native C methods there is a requirement to free the log object after use (using os_release). The pyoslog module handles this for you – there is no need to del or release these objects.

As noted above, while the macOS os_log API allows use of a format string with many methods, this name is required to be a C string literal. As a result, pyoslog hardcodes all format strings to "%{public}s".

The pyoslog module's tests require the pyobjc OSLog framework wrappers and the storeWithScope initialiser in order to verify output so, as a result, can only be run on macOS 12 or later.

After installing the OSLog wrappers (via python -m pip install pyobjc-framework-OSLog), navigate to the tests directory and run:

python -m unittest

Please note that if Console.app is live-streaming messages, some tests may fail. See test_logging.py for discussion about why this is the case.

At the time this module was created there were no alternatives available on PyPi. Since then, the macos-oslog module has been released, with broadly equivalent functionality to pyoslog, except for the need to manually release the log object. There is also os-signpost, which uses cython to provide the OSSignposter API, and could easily be extended to provide os_log functionality.

In addition, there are other options available if PyPi access is not seen as a constraint:

• apple_os_log_py
• pymacoslog
• loggy

Note that the pyobjc module OSLog is for reading from the unified logging system rather than writing to it (and as a result is used for testing pyoslog). A log.h binding is on that project's roadmap, but not yet implemented.

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