logging config with verboselogs and coloredlogs

log_config.py

#!/usr/bin/env python3
"""
Easliy set up a consistent logging configuration for all codes that use this
library.

The main code can be written as:

    import logging
    import coloredlogs
    import argparse

    ...

    parser = argparse.ArgumentParser(...)
    ...
    # Set up other parser arguments.
    ...
    this.module.configure_argparser(parser)
    args = parser.parse_args()
    this_module.log_config.install_with_args(args, coloredlogs)
    logger = logging.getLogger(__name__)
    ...
"""

import logging
import verboselogs

def install_with_args(coloredlogs, args=None):
    """
    Install the logging configuration by using the args (as output by
    argparse.ArgumentParser), and a coloredlogs module imported from the main
    program.
    """
    verboselogs.install()

    # Find the final log level
    if args:
        if args.quiet:
            for times in range(args.quiet):
                coloredlogs.decrease_verbosity()
        elif args.verbose:
            for times in range(args.verbose):
                coloredlogs.increase_verbosity()
        else:
            coloredlogs.set_level(args.log_level)
    else:
        coloredlogs.set_level('INFO')


    # Because bold black is not visible in solarized dark theme in
    # gnome-terminal, we make levelname without any formatting
    field_style = coloredlogs.DEFAULT_FIELD_STYLES
    field_style['levelname'] = {}

    # Make a format string depending on the final log level. See the logging
    # module reference for more details.
    format_str = "%(levelname)8s %(asctime)s.%(msecs)03d"
    if coloredlogs.get_level() < coloredlogs.level_to_number('INFO'):
        format_str += " %(name)s"
    if coloredlogs.get_level() <= coloredlogs.level_to_number('SPAM'):
        format_str += " %(pathname)s"
    if coloredlogs.get_level() <= coloredlogs.level_to_number('DEBUG'):
        format_str += " %(funcName)s():%(lineno)d"
    if coloredlogs.get_level() <= coloredlogs.level_to_number('VERBOSE'):
        format_str += " %(threadName)s"
    format_str += ": %(message)s"

    # Finally install it to the root logger, using the module imported from the
    # main program.
    coloredlogs.install(
            level=coloredlogs.get_level(),
            fmt=format_str,
            field_style=field_style)


def configure_argparser(parser):
    """Adds arguments to a argparser.ArgumentParser to control the verbosity"""
    log_config = parser.add_mutually_exclusive_group()

    log_config.add_argument(
        "--log-level",
        choices=[
            "CRITICAL",
            "ERROR",
            "WARNING",
            "NOTICE",
            "INFO",
            "VERBOSE",
            "DEBUG",
            "SPAM"],
        default="INFO",
        help="Set the log level")
    log_config.add_argument(
            "--verbose", "-v",
            action='count',
            help="Increase the verbosity")
    log_config.add_argument(
            "--quiet", "-q",
            action='count',
            help="Decrease the verbosity")