Singleton Logging Service

Logging service that is guaranteed to be a singleton. Based on Python logging, but every instantiation of LoggingService from any of an application's modules returns the same logger instance.

###Examples:

    from logging_service import LoggingService

    self.log = LoggingService()

    self.log.info("Constructing output file names...")
    self.log.err("Failed to construct output file names...")
    self.log.warn("Output file names are unusual...")
    self.log.debug("Constructing output file names foo.bar, fum.txt...")

This API is more primitive than the hierarchical native logging module, but hopefully simple to use. One can:

    - Log to a file,
    - The console, or
    - Both

For convenience, the logging levels logging.DEBUG, logging.INFO, etc. are available in this package as enums: LoggingLevel.DEBUG, LoggingLevel.INFO, etc. Just import LoggingLevel with LoggingService.

A single formatter is built in for info/debug/warn/err. Example:

my_module.py(290375): 2020-09-03 14:58:33,017;INFO: Start Epoch [1/50]

When first creating a LoggingService instance, the following options are available in the constructor; all are optional:

logging_level=LoggingLevel.INFO    # equivalent to the Python logging package's constants
logfile=None,                 # destination file; None implies console only
tee_to_console=True,          # if logfile is specified, also log to console
msg_identifier=None,          # shown at start of each msg; default is module name
rotating_logs=True,           # if logging to file, rotate log if size exceeded
log_size=1000000,             # max log size for rotation
max_num_logs=500,             # max number of full logs to retain
logger_name=None              # name for the logger instance

After creation a logger instance may only be modified like this:

- my_logger.logging_level = LoginLevel.<NEW_LEVEL>
- my_logger.log_file      = '/tmp/new_logfile'

where logging levels are the usual logging.INFO, logging.WARN, etc.