Python config parsing / access experiment.

config.ini

[DEFAULT]
num = 42
pi = 3.141312301928312039810
debug = no
on = yes
sleep = 2

[mqtt]
host = localhost
port = 1883

[database]
host = localhost
port = 5432
username = FOO
password = BAR

main.py

"""

This is a very simple config reader that includes support for the following
features:

* Parsing settings from a INI-style config file (using ConfigParser)
* It re-reads the config file on every attribute access (so you don't need to
  reload your software after a config update)
* It converts config entries to a reasonable datatype without you knowing
  in advance what those are (i.e. you don't have to write extra code for this)
* It uses dot notation to access entries within a section; i.e. conf.database.host
  or conf.database.username

Example usage:

    >>> config = Config("/path/to/config.ini")
    >>> config.debug
    True

    >>> config.database.host
    'localhost'

    >>> config.database.port
    5432

"""
import configparser
import re

from contextlib import contextmanager


class ConfigSection:
    """This class is a small wrapper for a ConfigParser section. It will
    attempt to convert data found in a config file to an appropriate data type;

    Supported data types include:

    - boolean
    - int
    - float
    - string

    """

    def __init__(self, section):
        self.section = section

    def _to_datatype(self, result):
        # Try converting the requested config entry to it's appropriate data type.
        if result in ["yes", "on", "true"]:
            return True
        elif result in ["no", "off", "false"]:
            return False
        elif result.isdigit():
            return int(result)
        elif re.match("^\d+?\.\d+?$", result):
            return float(result)
        else:
            return result

    def __getattr__(self, name):
        return self._to_datatype(self.section[name])


class Config:
    """This class is a ConfigParser wrapper that allows you to access configuration
    settings using a dot notation; for example:

        >>> conf = Config("your_config.ini")
        >>> conf.DEBUG  # specified as "on" or "yes"
        True

        >>> conf.database.host
        'localhost'

        >>> conf.database.port
        5432

    """

    def __init__(self, filename):
        self.filename = filename
        self.config = configparser.ConfigParser()
        self._read()

    def _read(self):
        self.config.read(self.filename)

    def __getattr__(self, key):
        return self._read_from_section(key)

    def _read_from_section(self, key):
        self._read()
        try:
            section = self.config[key]
            return ConfigSection(section)
        except KeyError:
            # key is not a section, it's likely a default value
            section = ConfigSection(self.config["DEFAULT"])
            return getattr(section, key)

    @contextmanager
    def section(self, key):
        yield self._read_from_section(key)


if __name__ == "__main__":
    #
    # This is a essentially a simple test that reads from the included
    # config.ini file & continues to print config data forever.
    #
    import time

    conf = Config("config.ini")

    print("-" * 40)
    print("Edit the included config.ini file & watch\nyour results update below!")
    print("-" * 40)
    time.sleep(2)

    while True:
        sleep = conf.sleep
        print(f"Is this thing on!? {conf.on}")
        print(f"conf.debug -> {conf.debug} /// {type(conf.debug)}")
        print(f"conf.num   -> {conf.num}  /// {type(conf.num)}")
        print(f"conf.pi    -> {conf.pi}  /// {type(conf.pi)}")

        host = conf.database.host
        port = conf.database.port
        user = conf.database.username
        password = conf.database.password
        print(f"DB         -> {user}:{password}@{host}:{port}")

        print("\nUsing contxt manager to read the MQTT section... ")
        with conf.section("mqtt") as section:
            print(f"MQTT: {section.host}:{section.port}")

        print("-" * 40)
        time.sleep(sleep)

requirements.txt

clog==0.2.3
ipython==7.8.0