logger_tt 1.4.2

Make logging simple, log even exception that you forgot to catch

Logger_tt

Make configuring logging simpler and log even exceptions that you forgot to catch.

Install

• From PYPI: pip install logger_tt
• From Github: clone or download this repo then python setup.py install

Overview:

In the most simple case, add the following code into your main python script of your project:

from logger_tt import setup_logging    

setup_logging()

Then from any of your modules, you just need to get a logger and start logging.

from logging import getLogger

logger = getLogger(__name__)

logger.debug('Module is initialized')
logger.info('Making connection ...')

This will provide your project with the following default log behavior:

• log file: Assume that your working directory is project_root, log.txt is stored at your project_root/logs/ folder. If the log path doesn't exist, it will be created. The log file is time rotated at midnight. A maximum of 15 dates of logs will be kept. This log file's level is DEBUG.
  The log format is [%(asctime)s] [%(name)s %(levelname)s] %(message)s where time is %Y-%m-%d %H:%M:%S.
  Example: [2020-05-09 00:31:33] [myproject.mymodule DEBUG] Module is initialized

• console: log with level INFO and above will be printed to stdout of the console.
  The format for console log is simpler: [%(asctime)s] %(levelname)s: %(message)s.
  Example: [2020-05-09 00:31:34] INFO: Making connection ...

• urllib3 logger: this ready-made logger is to silent unwanted messages from requests library.

• suppressed logger: exchangelib. This sets logging level of exchangelib logger to WARNING.
  This is another way to silent unwanted messages from other module, read below for details.

• root logger: if there is no logger initialized in your module, this logger will be used with the above behaviors. This logger is also used to log uncaught exception in your project. Example:

raise RecursionError

# log.txt
[2020-05-31 19:16:01] [root ERROR] Uncaught exception
Traceback (most recent call last):
  File "D:/MyProject/Echelon/eyes.py", line 13, in <module>
    raise RecursionError
    => var_in = Customer(name='John', member_id=123456)
    => arg = (456, 789)
    => kwargs = {'my_kw': 'hello', 'another_kw': 'world'}
RecursionError

• context logging: When an exception occur, variables used in the line of error are also logged.
  If the line of error is raise {SomeException}, then local variables are also logged.
  To always log full local variables, pass full_context=True to setup_logging.

Usage:

All configs are done through setup_logging function:

setup_logging(config_path="", log_path="", 
              capture_print=False, strict=False, guess_level=False,
              full_context=False,
              suppress_level_below=logging.WARNING)

1. You can overwrite the default log path with your own as follows:

   setup_logging(log_path='new/path/to/your_log.txt')
   

2. You can config your own logger and handler by providing either yaml or json config file as follows:

   setup_logging(config_path='path/to/.yaml_or_.json')
   

   Without providing a config file, the default config file with the above default log behavior is used. You could copy log_conf.yaml or log_conf.json shipped with this package to start making your version.

   Warning: To process .yaml config file, you need pyyaml package: pip install pyyaml

3. Capture stdout:

   If you have an old code base with a lot of print(msg) or sys.stdout.write(msg) and don't have access or time to refactor them into something like logger.info(msg), you can capture these msg and log them to file, too.

   To capture only msg that is printed out by print(msg), simply do as follows:

   setup_logging(capture_print=True)
   

   Example:

   print('To be or not to be')
   sys.stdout.write('That is the question')
   

   # log.txt
   [2020-05-09 11:42:08] [PrintCapture INFO] To be or not to be
   

   ---

   Yes, That is the question is not captured. Some libraries may directly use sys.stdout.write to draw on the screen (eg. progress bar) or do something quirk. This kind of information is usually not useful for users. But when you do need it, you can capture it as follows:

   setup_logging(capture_print=True, strict=True)
   

   Example:

   sys.stdout.write('The plane VJ-723 has been delayed')
   sys.stdout.write('New departure time has not been scheduled')
   

   # log.txt
   [2020-05-09 11:42:08] [PrintCapture INFO] The plane VJ-723 has been delayed
   [2020-05-09 11:42:08] [PrintCapture INFO] New departure time has not been scheduled
   

   ---

   As you have seen, the log level of the captured message is INFO . What if the code base prints something like An error has occurred. Abort operation. and you want to log it as Error? Just add guess_level=True to setup_logging().

   setup_logging(capture_print=True, guess_level=True)
   

   Example:

   print('An error has occurred. Abort operation.')
   print('A critical error has occurred during making request to database')
   

   # log.txt
   [2020-05-09 11:42:08] [PrintCapture ERROR] An error has occurred. Abort operation.
   [2020-05-09 11:42:08] [PrintCapture CRITICAL] A critical error has occurred during making request to database
   

   Note: Capturing stdout ignores messages of blank line. That means messages like \n\n or (spaces) will not appear in the log. But messages that contain blank line(s) and other characters will be fully logged. For example, \nTo day is a beautiful day\n will be logged as is.

4. Exception logging:

   Consider the following error code snippet:

   API_KEY = "asdjhfbhbsdf82340hsdf09u3ionf98230234ilsfd"
   TIMEOUT = 60
   
   class MyProfile:
       def __init__(self, name):
           self.my_boss = None
           self.name = name
   
   def my_faulty_func(my_var, *args, **kwargs):
       new_var = 'local scope variable'
       me = MyProfile('John Wick')
       boss = MyProfile('Winston')
       me.my_boss = boss
       print(f'Information: {var} and {me.my_boss.name}' 
              ' at {me.my_boss.location} with {API_KEY}')
   
   if __name__ == '__main__':
       cpu_no = 4
       max_concurrent_processes = 3
       my_faulty_func(max_concurrent_processes, 'ryzen 7', freq=3.4)
   

   In our hypothetical code above,print function will raise an exception. This exception, by default, will not only be logged but also analyzed with objects that appeared in the line:

   [2020-06-06 09:36:01] ERROR: Uncaught exception:
   Traceback (most recent call last):
     File "D:/MyProject/AutoBanking/main.py", line 31, in <module>
       my_faulty_func(max_concurrent_processes, 'ryzen 7', freq=3.4)
        |-> my_faulty_func = <function my_faulty_func at 0x0000023770C6A288>
        |-> max_concurrent_processes = 3
   
     File "D:/MyProject/AutoBanking/main.py", line 25, in my_faulty_func
       print(f'Information: {var} and {me.my_boss.name}'
              ' at {me.my_boss.location} with {API_KEY}')
        |-> me.my_boss.name = 'Winston'
        |-> me.my_boss.location = '!!! Not Exists'
        |-> (outer) API_KEY = 'asdjhfbhbsdf82340hsdf09u3ionf98230234ilsfd'
   NameError: name 'var' is not defined
   

   Note: look at the print(f'Information... line, logger-tt print this error line different from normal python traceback! With normal traceback, multi-line python statement has its only first line printed out. With logger-tt, full statement is grabbed for you.

   For each level in the stack, any object that appears in the error line is shown with its readable representation. This representation may not necessarily be __repr__. The choice between __str__ and __repr__ are as follows:

   • __str__ : __str__ is present and the object class's __repr__ is default with <class name at Address>.
   • __repr__: __str__ is present but the object class's __repr__ is anything else, such as ClassName(var=value).
     Also, when __str__ is missing, even if __repr__ is <class name at Address>, it is used.

   Currently, if an object doesn't exist and is directly accessed, as var in this case, it will not be shown up. But if it is attribute accessed with dot ., as location in me.my_boss.location, then its value is an explicit string '!!! Not Exists'.

   As you may have noticed, a variable API_KEY has its name prefixed with outer.
   This tells you that the variable is defined in the outer scope, not local.

   More often than not, only objects in the error line are not sufficient to diagnose what has happened. You want to know what the inputs of the function were. You want to know what the intermediate calculated results were. You want to know other objects that appeared during runtime, not only local but also outer scope. In other words, you want to know the full context of what has happened. logger-tt is here with you:

   setup_logging(full_context=True)
   

   With the above hypothetical code snippet, the error log becomes the following:

   [2020-06-06 10:35:21] ERROR: Uncaught exception:
   Traceback (most recent call last):
     File "D:/MyProject/AutoBanking/main.py", line 31, in <module>
       my_faulty_func(max_concurrent_processes, 'ryzen 7', freq=3.4)
        |-> my_faulty_func = <function my_faulty_func at 0x0000019E3599A288>
        |-> max_concurrent_processes = 3
        => __name__ = '__main__'
        => __doc__ = None
        => __package__ = None
        => __loader__ = <_frozen_importlib_external.SourceFileLoader object at 0x0000019E35840E48>
        => __spec__ = None
        => __annotations__ = {}
        => __builtins__ = <module 'builtins' (built-in)>
        => __file__ = 'D:/MyProject/AutoBanking/main.py'
        => __cached__ = None
        => setup_logging = <function setup_logging at 0x0000019E35D111F8>
        => getLogger = <function getLogger at 0x0000019E35BC7C18>
        => logger = <Logger __main__ (DEBUG)>
        => API_KEY = 'asdjhfbhbsdf82340hsdf09u3ionf98230234ilsfd'
        => TIMEOUT = 60
        => MyProfile = <class '__main__.MyProfile'>
        => cpu_no = 4
   
     File "D:/MyProject/AutoBanking/main.py", line 25, in my_faulty_func
       print(f'Information: {var} and {me.my_boss.name} at {me.my_boss.location} with {API_KEY}')
        |-> me.my_boss.name = 'Winston'
        |-> me.my_boss.location = '!!! Not Exists'
        |-> (outer) API_KEY = 'asdjhfbhbsdf82340hsdf09u3ionf98230234ilsfd'
        => my_var = 3
        => args = ('ryzen 7',)
        => kwargs = {'freq': 3.4}
        => new_var = 'local scope variable'
        => me = <__main__.MyProfile object at 0x0000019E35D3BA48>
        => boss = <__main__.MyProfile object at 0x0000019E35D3B9C8>
   NameError: name 'var' is not defined
   

   Additional objects that not appear in the error line are prefixed with =>.

5. try-except exception logging:

   exception context logging also applies for try-except block. This means that if you call logger.exception() inside except block, you would have all variables' value at the line of exception. For example,

   def my_faulty_func():
       a = 10
       b = 0
       c = a/b
       return c
   
   def my_main():
       try:
           my_faulty_func()
       except Exception as e:
           logger.exception('some error has occured')
           print('Clean up resource')
   
   my_main()
   

   Then the log will show up as follows:

   [2020-06-12 21:37:00] ERROR: some error has occured
   Traceback (most recent call last):
     File "D:/MyProject/exception_log.py", line 19, in my_main
       my_faulty_func()
        |-> my_faulty_func = <function my_faulty_func at 0x000001875DD4B168>
   
     File "D:/MyProject/exception_log.py", line 13, in my_faulty_func
       c = a / b
        |-> a = 10
        |-> b = 0
   ZeroDivisionError: division by zero
   Clean up resource
   

   Note: As in python's logging document, logger.exception() should only be called from an exception handler, eg. inside except block.

   You don't need to pass exception object to logger.exception(). It already knows how to get a traceback internally. This enable you to pass any string in as a hint or a short description of what may have happened.
   Otherwise, passing exception object, as logger.exception(e), will cause the first line of error report to be the message of exception. In the case of the above example, it would be come [2020-06-12 21:37:00] ERROR: division by zero.

6. Silent unwanted logger:

   Third party modules also have logger and their messages are usually not related to your code. A bunch of unwanted messages may hide the one that come from your own module. To prevent that and also reduce log file size, we need to silent unwanted loggers.

   There are two ways to silent a logger with config file:

   • Create a new logger: in logger section of config file, add a new logger whose name is the same with the one you want to silent. Set it level to WARNING or above. If you add handlers, you should also set propagate to no or False. Otherwise, the same message may be logged multiple times. Ex:

     urllib3:
       level: WARNING
       handlers: [console, error_file_handler]
       propagate: no
     

     Above setting only allow messages with level WARNING and above to be processed. Usually that is enough to silent most of unwanted messages. If you need to silent more messages, try ERROR or CRITICAL.

   • Add logger's name to suppress list: Then a new logger with level default to WARNING will be automatically created for you. Ex:

     suppress: [exchangelib, urllib3]
     

     If you need to suppress at even higher level, use suppress_level_below in setup_logging. For example suppress any message below ERROR level that comes from loggers in suppress list:

     setup_logging(suppress_level_below=logging.ERROR)
     

Sample config:

1. Yaml format:

   log_config.yaml:

   version: 1
   disable_existing_loggers: False
   formatters:
     simple:
       format: "[%(asctime)s] [%(name)s %(levelname)s] %(message)s"
       datefmt: "%Y-%m-%d %H:%M:%S"
     brief: {
       format: "[%(asctime)s] %(levelname)s: %(message)s"
       datefmt: "%Y-%m-%d %H:%M:%S"
   handlers:
     console:
       class: logging.StreamHandler
       level: INFO
       formatter: simple
       stream: ext://sys.stdout
   
     error_file_handler:
       class: logging.handlers.TimedRotatingFileHandler
       level: DEBUG
       formatter: simple
       filename: logs/log.txt
       backupCount: 15
       encoding: utf8
       when: midnight
   
   loggers:
     urllib3:
       level: WARNING
       handlers: [console, error_file_handler]
       propagate: no
   
   root:
     level: DEBUG
     handlers: [console, error_file_handler]
   
   suppress: [exchangelib]
   

2. Json format:

log_config.json:

{
  "version": 1,
  "disable_existing_loggers": false,
  "formatters": {
    "simple": {
      "format": "[%(asctime)s] [%(name)s %(levelname)s] %(message)s",
      "datefmt": "%Y-%m-%d %H:%M:%S"
    },
    "brief": {
      "format": "[%(asctime)s] %(levelname)s: %(message)s",
      "datefmt": "%Y-%m-%d %H:%M:%S"
    }
  },

  "handlers": {
    "console": {
      "class": "logging.StreamHandler",
      "level": "INFO",
      "formatter": "brief",
      "stream": "ext://sys.stdout"
    },

    "error_file_handler": {
      "class": "logging.handlers.TimedRotatingFileHandler",
      "level": "DEBUG",
      "formatter": "simple",
      "filename": "logs/log.txt",
      "backupCount": 15,
      "encoding": "utf8",
      "when": "midnight"
    }
  },

  "loggers": {
    "urllib3": {
      "level": "ERROR",
      "handlers": ["console", "error_file_handler"],
      "propagate": false
    }
  },

  "root": {
    "level": "DEBUG",
    "handlers": ["console", "error_file_handler"]
  },

  "suppress": ["exchangelib"]
}

changelog

1.4.2

To prevent exception during logging, the following actions have been applied:

• Catch exception while parsing for object's value (property of a class)
• Catch exception while evaluating __repr__ and __str__ of object
• Disable logging while inspecting objects' value and representation
• Disable logging after an uncaught exception is logged. Because the interpreter is shutting down, objects get deleted. Logging put inside magic function __del__ will raise error.

1.4.1

• Fix print_capture ignoring print() line in global scope due to lacking code_context frame
• If __str__ of an object has multiple lines, also indent the second line and so on accordingly.
• If there is an exception during getting object's representation, return !!! Attribute error instead of Error in sys.excepthook

1.4.0

• Add an extra field suppress in config file. Any logger's name appeared in this list will have its messages suppressed.

1.3.2

• change extended ascii dash ─ to normal dash - so that it is displayed consistently in different encoding

1.3.1

• change extended ascii vertical bar ├ to normal bar | so that it is displayed consistently in different encoding

1.3.0

• Exception analyzing now fetch full multi-line python statement. This means that variables lie at seconds and below of the same statement can also be seen without the need of full_context=True.

1.2.1

• Extend logging context to logger.exception() as well. Now you can do try-except a block of code and still have a full context at error line.

1.2.0

• Add logging context for uncaught exception. Now automatically log variables surrounding the error line, too.
• Add test cases for logging exception

1.1.1

• Fixed typos and grammar
• Add config file sample to README
• using full name log_config.json instead of log_conf.json, the same for yaml file
• add test cases for capture print

1.1.0

• Add capture print functionality with guess level for the message.