How to provide a default configuration which individual points may be overriden in a custom configuration file (to improve and explain)

conf.py

"""
================
euscans.settings
================

Provides settings customization and public configuration object

[DEPRECATED] I released the ``pyflexconfig`` package on PyPI that rationalizes and improves this boilerplate.

https://pypi.org/project/pyflexconfig/
"""

from argparse import Namespace
import logging.config
import os

from euscans import LOG
from .utils import execfile, CommandBase

this_directory = os.path.dirname(os.path.abspath(__file__))
default_settings_file = os.path.join(this_directory, 'defaultsettings.py')
assert os.path.isfile(default_settings_file), "Broken package: File '{}' is missing".format(default_settings_file)

def get_config(*files):
    """Provides a :class:`argparse.Namespace` configuration object that merges
    all uppercase globals in Python ``files`` that don't start with '_'

    Note:
        Values from a file override values of same name provided by a previous file.

    Args:
        files (Iterable(str)): Paths to all config files

    Returns:
        argparse.Namespace: Merged configuration data

    Examples:

        Preparation

        >>> import os, tempfile
        >>> CONFIG1 = '''DATA1 = 10
        ... ignored = 100
        ... _IGNORED = 1000'''
        >>> CONFIG2 = '''DATA1 = 100
        ... EXTRA = 100'''
        >>> config1, path_config1 = tempfile.mkstemp('.py')
        >>> with os.fdopen(config1, 'w') as config1:
        ...     _ = config1.write(CONFIG1)
        >>> config2, path_config2 = tempfile.mkstemp('.py')
        >>> with os.fdopen(config2, 'w') as config2:
        ...     _ = config2.write(CONFIG2)

        Make the conf.

        >>> conf = get_config(path_config1, path_config2)
        >>> conf.DATA1
        100
        >>> conf.EXTRA
        100
        >>> hasattr(conf, 'ignored')
        False
        >>> hasattr(conf, '_IGNORED')
        False

        Cleaning...

        >>> os.unlink(path_config1)
        >>> os.unlink(path_config2)

    """
    conf_globals = {}
    conf_locals = {}
    for file_ in files:
        execfile(file_, conf_globals, conf_locals)
    conf_locals = {name: value for name, value in conf_locals.items()
                   if name.isupper() and not name.startswith('_')}
    return Namespace(**conf_locals)


conf = None


def bootstrap():
    """Bootstraps the global ``conf`` object
    """
    global conf

    # One shot function in process
    if conf is not None:
        return

    is_file = os.path.isfile

    # Standard settings
    settings_files = (default_settings_file,)

    # Custom settings
    custom_settings_file = os.environ.get('EUSCANS_CONFIG_FILE')
    if custom_settings_file is not None:
        assert is_file(custom_settings_file), "Custom settings file '{}' does not exist".format(custom_settings_file)
        settings_files += (custom_settings_file,)

    LOG.debug("Reading the settings from %s", settings_files)

    conf = get_config(*settings_files)
    logging.config.dictConfig(conf.LOGGING)
    return


class DumpConfigCommand(CommandBase):
    name = 'dumpsettings'
    help = "Prints the default settings to stdout. Which may be edited to make your custom settings"

    def run(self, args, extra_args):
        with open(default_settings_file, 'r') as fh:
            for line in fh:
                stripped = line.strip()
                if stripped.startswith('#') or len(stripped) == 0:
                    print(line, end='')
                else:
                    print('#'+line, end='')