__main__.py

from .util.logging import root_logger as logger
from .util.config import FileConfig, GCloudFileConfig, EnvironmentalVariableConfig, CliConfig, ConfigCombiner

config = ConfigCombiner(
    [
        FileConfig,
        GCloudFileConfig,
        EnvironmentalVariableConfig,
        CliConfig
    ],
    parent_logger=logger
)

print(config.log_level)

config.py

import logging, pathlib, json, sys, subprocess, os
from .. import version
from .logging import root_logger as logger


class Config(object):
    def __init__(self, parent_logger=logger):
        self.log = parent_logger.getChild(self.__class__.__name__)
        self.config = {"log_level": "INFO"}

    def __getattr__(self, attr):
        try:
            return self.config[attr]
        except KeyError:
            return None

    def __setattr__(self, attr, value):
        if attr in ["log", "config"]:
            super(Config, self).__setattr__(attr, value)
        else:
            self.config[attr] = value


class FileConfig(Config):
    def __init__(self, *args, path="config.json", required=False, **kwargs):
        super(FileConfig, self).__init__(*args, **kwargs)
        self._load_config(path, required=required)

    def _load_config(self, path, required=False):
        path = pathlib.Path(path)
        if path.is_file():
            self.log.info("Config file found. - {}")
            with open(path, 'r') as f:
                config = json.load(f)
            self.config.update(config)
        else:
            log = "Config file not found. - {}".format(path)
            if required:
                self.log.fatal(log)
                raise FileNotFoundError(path)
            else:
                self.log.info(log)


class GCloudFileConfig(Config):
    def __init__(self, *args, **kwargs):
        super(GCloudFileConfig, self).__init__(*args, **kwargs)
        project_name = self._get_cloud_project_name()
        file_config = FileConfig(path=f"{project_name}.json", required=False, parent_logger=self.log)
        self.config.update(file_config.config)

    @staticmethod
    def _get_cloud_project_name():
        call = "gcloud config get-value project"
        result = subprocess.check_output(call.split(" "), stderr=open(os.devnull, 'wb'))
        project_name = result.decode('utf-8').strip()
        return project_name


class EnvironmentalVariableConfig(Config):
    def __init__(self, *args, **kwargs):
        super(EnvironmentalVariableConfig, self).__init__(*args, **kwargs)
        environmental_variable_config = self._get_environmental_key_values()
        self.log.info(f"Checking for environmental variables. ( {version.NAME.upper()}_KEY )")
        if environmental_variable_config:
            self.log.info(environmental_variable_config)
        self.config.update(environmental_variable_config)

    @staticmethod
    def _get_environmental_key_values():
        def parse_environmental_variables():
            prefix = version.NAME.upper() + "_"
            for key in os.environ:
                if key.startswith(prefix) and len(key) > len(prefix):
                    value = os.environ[key]
                    key = key[len(prefix):].lower()
                    yield key, value
        return dict(parse_environmental_variables())


class CliConfig(Config):
    def __init__(self, *args, **kwargs):
        super(CliConfig, self).__init__(*args, **kwargs)

        cli_config = self._get_cli_config()
        self.log.debug(cli_config)

        # if config file specified, load that
        if 'config' in cli_config:
            self.log.info("Config file specified. - {}".format(cli_config['config']))
            file_config = FileConfig(path=cli_config['config'], required=True, parent_logger=self.log)
            self.config.update(file_config.config)

        self.config.update(cli_config)

    @staticmethod
    def _get_cli_config():
        def get_cli_key_vals():
            for i, arg in enumerate(sys.argv):
                if "--" in arg and len(sys.argv)-1 > i:
                    key = arg[2:]
                    value = sys.argv[i+1]
                    yield key, value

        return dict(get_cli_key_vals())


class ConfigCombiner(Config):
    def __init__(self, config_classes, *args, **kwargs):
        super(ConfigCombiner, self).__init__(*args, **kwargs)
        for config_class in config_classes:
            config = config_class(*args, parent_logger=self.log)
            self.config.update(config.config)

output.log

(venv) zac@zwafer:~/work/PyCharmProjects/paste_pizza$ python3 -m paste_pizza
20190506T015138.109483Z |    DEBUG | paste_pizza | Starting up. - 20190505_0_dev
20190506T015138.117844Z |     INFO | paste_pizza.ConfigCombiner.FileConfig | Config file not found. - config.json
20190506T015138.334013Z |     INFO | paste_pizza.ConfigCombiner.GCloudFileConfig.FileConfig | Config file not found. - paste-pizza.json
20190506T015138.334285Z |     INFO | paste_pizza.ConfigCombiner.EnvironmentalVariableConfig | Checking for environmental variables. ( PASTE_PIZZA_KEY )
20190506T015138.334379Z |     INFO | paste_pizza.ConfigCombiner.EnvironmentalVariableConfig | {'log_level': 'INFO'}
20190506T015138.334475Z |    DEBUG | paste_pizza.ConfigCombiner.CliConfig | {}
INFO
(venv) zac@zwafer:~/work/PyCharmProjects/paste_pizza$ python3 -m paste_pizza --config cli.json --log_level DEBUG
20190506T015224.611133Z |    DEBUG | paste_pizza | Starting up. - 20190505_0_dev
20190506T015224.619668Z |     INFO | paste_pizza.ConfigCombiner.FileConfig | Config file not found. - config.json
20190506T015224.836832Z |     INFO | paste_pizza.ConfigCombiner.GCloudFileConfig.FileConfig | Config file not found. - paste-pizza.json
20190506T015224.837123Z |     INFO | paste_pizza.ConfigCombiner.EnvironmentalVariableConfig | Checking for environmental variables. ( PASTE_PIZZA_KEY )
20190506T015224.837206Z |     INFO | paste_pizza.ConfigCombiner.EnvironmentalVariableConfig | {'log_level': 'INFO'}
20190506T015224.837308Z |    DEBUG | paste_pizza.ConfigCombiner.CliConfig | {'config': 'cli.json', 'log_level': 'DEBUG'}
20190506T015224.837390Z |     INFO | paste_pizza.ConfigCombiner.CliConfig | Config file specified. - cli.json
20190506T015224.837522Z | CRITICAL | paste_pizza.ConfigCombiner.CliConfig.FileConfig | Config file not found. - cli.json
Traceback (most recent call last):
  File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/zac/work/PyCharmProjects/paste_pizza/paste_pizza/__main__.py", line 11, in <module>
    parent_logger=logger
  File "/home/zac/work/PyCharmProjects/paste_pizza/paste_pizza/util/config.py", line 112, in __init__
    config = config_class(*args, parent_logger=self.log)
  File "/home/zac/work/PyCharmProjects/paste_pizza/paste_pizza/util/config.py", line 91, in __init__
    file_config = FileConfig(path=cli_config['config'], required=True, parent_logger=self.log)
  File "/home/zac/work/PyCharmProjects/paste_pizza/paste_pizza/util/config.py", line 27, in __init__
    self._load_config(path, required=required)
  File "/home/zac/work/PyCharmProjects/paste_pizza/paste_pizza/util/config.py", line 40, in _load_config
    raise FileNotFoundError(path)
FileNotFoundError: cli.json