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Aggregate Python log messages into a single log entry.

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Aggregate messages to produce a log entry representing a single event or procedure. The purpose of this module is to easily asssociate log messages together that belong together.

import logging
from logtrace import LogTrace

logger = logging.getLogger(__name__)
trace = LogTrace(logger=logger)

trace.add("Let's get started")
...
trace.add("Later, something else happens")
...
trace.add("And finally...")

trace.emit()

You get a single log entry like this:

[05/Jan/2018 11:11:00] DEBUG [21, .30s] Let's get started; [65, .132s] Later, something else happens; [75, .330s] And finally...

Install

pip install logtrace

Note that this only suppports Python 3. Let me know if anyone wants support for Python 2. There are no dependencies outside the Python Standard Library for this module.

Example

Logs can be hard to read because you have cases where you log information as you go through a procedure. These log entries get scattered with all the other logs from other processes. You end up having to search for related entries possibly implanting identifying information in each one to tie them together. LogTrace fixes this problem by letting you collect logs and then output once. Take the example of a token authentication procedure where transient tokens are required to be authenticated. You want to record the following events:

  • Check the HTTP header info with the token
  • What table are we going to use to check the token?
  • Did the token service authenticate the token?
  • Is the token in a local cache?
  • Successfully authenticated?

The following records five separate instances where you would have called logger.info() with a line number and the time in seconds since constructing the LogTrace object [<lineno>, <secs>s]:

[12:12:54] INFO [132, 0.0006s] auth header: [b'Token', b'2c59999137******************************']; [132, 0.0007s] authenticate key, model: <class 'tastypie.models.ApiKey'>; [132, 0.1057s] token renewal for API call confirmed; [132, 0.1078s] got key from token table: paul; [163, 0.1079s] Successfully authenticated

Details

We respect logging levels. So, the overhead of using LogTrace is minimal if your log level is not effective. If your log level is logging.INFO and you call logtrace.emit_debug(), almost all overhead is avoided minus some function call overhead and one or two conditional expressions.

What LogTrace is not: This is not a logging framework. LogTrace uses the standard Python logging module. All your configuration to logging is going to be used by LogTrace. All your handlers are going to act exactly as before. If you use a framework like Django, you use it just like you do now. No changes whatever are required to your logging configuration.

We also provide other features like

  • Easily generate a UUID for the logged event.
  • Timing for each message since LogTrace was created.
  • Frame information for each part message, like filename, function, lineno
  • Any logging mechanism can be used, not just standard Python logging.
  • Pass structured data (JSON).

We wanted to provide something that works in perfect harmony with the existing Python logging module without unnecessary duplication of features and no external dependencies (outside the PSL).

LogTrace(logger=None,      # we'll emit output here
         delimiter="; ",   # delimiter between messages
         tag='',           # add a non-unique label
         unique_id=False,  # create a uuid to identify the log?
         verbosity='v'     # level of output for frame information
        )
  • logger: the standard logger returned from import logging; logger   = logging.getLogger(__name__). You can create a LogTrace() without a logger in which case it creates with the value of __name__.
  • delimiter: the character(s) used between messages
  • tag: This is a convenience to tell LogTrace() to use hash+tag at the start of every entry after calling .emit() for ease of searching.
  • unique_id: generate a uuid to associate with the final message output.
  • verbosity: v, vv, vvv for three levels of verbosity when adding frame information

LogTrace.get_uid(): return the unique id. If one has not been set during construction of the LogTrace, a uuid is generated. Otherwise, it returns the existing one.

LogTrace.set_uid(uid): Set a unique id. This can be done by constructing LogTrace() with unique_id=True. This takes normally either a uuid or str argument.

LogTrace.add(msg, data, backup): Add a message to the list. This will get frame information for the call depending on the verbosity level.

LogTrace.emit_string(): return a string that is the final log message.

LogTrace.emit(): call logger.debug(message)

LogTrace.emit_error(): call logger.error(message)

LogTrace.emit_info(): call logger.info(message)

LogTrace.emit_debug(): call logger.debug(message)

LogTrace.emit_warning(): call logger.warning(message)

LogTrace.emit_critical(): call logger.critical(message)

When the LogTrace is created, time.time() is recorded. Whenever LogTrace.add() is called, the start time is subtracted from the current time when the message is added. The final message prints the number of seconds since creating.

You probably want to avoid including LogTrace.add() in loops. You also probably want to create it as a local, not a module-level variable. Pass it as a method argument rather than using a module level instance. If you do want to re-use a LogTrace and clear messages, you can call LogTrace.clear(). But be aware the uid might need to be reset depending on your application requirements.

Extra Data

LogTrace.add() has an optional parameter data that takes a dictionary. We keep a dict in the object and update() it whenever the data parameter is used. This doesn’t do anything within LogTrace itself other than maintain the data member variable. But you can accumulate data and later ship the data to a service like AWS S3 or whatever, like this:

logger.info(trace.emit_string(), extra=trace.data)

This would be useful if you are using a logging handler that ships the logging.LogRecord as JSON to some service like a document oriented data store, Elasticsearch, etc.

Testing

pip install pytest
cd logtrace
pytest test.py --verbose

or

python3 logtrace/test.py

Performance

LogTrace() appends to a list of strings everytime you call add(). But it firstly calls inspect.getFrameInfo() and builds the string with that information. When emit() is called, it concatenates all the strings in the list separated by delimiter and then calls logger.info() or whatever method is appropriate. If the effective level is not the current level for the method, then the list will be empty and it won’t do the call to the logger method.

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0.1.1

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