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I have a settings file, which is loaded in once and takes the values from the settings json file and uses them as the attribute values. I was thinking of using the @property instead of overriding __getattribute__ but I feel as if there is a better, more elegant solution. Note that the application it is used in is multi-threaded.

settings.py

class SettingsMeta(type, JsonFileWrapperBase):
    _file_path = os.path.join(os.getcwd(), "..", "data", "settings.json")

    # Declarations to avoid PyCharm highlighting
    manga_save_dir, database_path, total_scrapper_threads, log_file = None, None, None, None

    _default_data = {
        "manga_save_dir": r"D:\dir",
        "database_path": r"D:\db.sqlite3",
        "log_file": os.path.join(os.getcwd(), "..", "data", "log.log"),

        "total_scrapper_threads": 1
    }

    @classmethod
    def __getattribute__(mcs, item):
        data = mcs._get_data()

        if item in data:
            return data[item]

        elif hasattr(mcs, item):
            return getattr(mcs, item)

        raise AttributeError(f"Settings has no attribute {item}")


class Settings(metaclass=SettingsMeta):
    pass

json_file_wrapper_base.py

class JsonFileWrapperBase:
    _loaded_data = None

    _file_path = ""
    _default_data = ""

    @classmethod
    def _write_default(cls):
        cls._write_data(cls._default_data)

    @classmethod
    def _write_data(cls, d):
        os.makedirs(os.path.dirname(os.path.abspath(cls._file_path)), exist_ok=True)

        try:
            with open(cls._file_path, "w") as f:
                json.dump(d, f)

        except FileNotFoundError as e:
            print(e)

    @classmethod
    def _get_data(cls):
        """
        Reads and caches the JSON file, if the file has already been cached then return the cached file, I cache
        the file to avoid users editing the file during execution and causing errors
        """

        # File has not been cached yet
        if cls._loaded_data is None:
            cls._read_file()

        return cls._loaded_data

    @classmethod
    def _read_file(cls) -> bool:
        assert cls._loaded_data is None, "_read_file should only be called once per object"

        # File doesn't exist or is not valid
        if not os.path.isfile(cls._file_path):
            cls._write_default()

        try:
            with open(cls._file_path, "r") as f:
                data = json.load(f)

                print(f"Log: Loaded {cls._file_path}")

                cls._loaded_data = data

        except FileNotFoundError as e:
            print(e)

            return False

        return True
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  • 1
    \$\begingroup\$ Please add your imports. This is especially important since you use JsonFileWrapperBase._get_data. \$\endgroup\$ – Graipher Sep 2 '19 at 15:46
  • 1
    \$\begingroup\$ I don't think the base class is relevant to my question about best practises forwarding values from JSON but I added it to my question neverthless. \$\endgroup\$ – Joshua Nixon Sep 2 '19 at 15:49
1
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Pathlib

Use it. It makes stuff like this:

os.path.join(os.getcwd(), "..", "data", "log.log"),

much nicer. It can also avoid this kind of thing:

"D:\dir"

namely, OS-specific directory separators. If you ever hope to have this be cross-platform, you'll want to remove your backslashes and use the libraries for path manipulation.

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4
  • \$\begingroup\$ OK. First thing is that the base class is in a different file. i only added due to a comment (I'll make it clearer in my question). Second, the assert is a very last resort I used for debugging, It will never be called. Thirdly, as you can see I use a metaclass as solely overriding __getattribute__ doesn't work for which mcs is standard. \$\endgroup\$ – Joshua Nixon Sep 2 '19 at 16:32
  • \$\begingroup\$ It was an formatting error regarding your assert comment. You haven't actually answered my question regarding forwarding values from JSON. \$\endgroup\$ – Joshua Nixon Sep 2 '19 at 16:40
  • \$\begingroup\$ That's true! And it doesn't matter - refer to codereview.meta.stackexchange.com/questions/5773/… \$\endgroup\$ – Reinderien Sep 2 '19 at 16:43
  • \$\begingroup\$ Ok, thats fair enough. \$\endgroup\$ – Joshua Nixon Sep 2 '19 at 16:45

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