* TIL: Initiate Config class in Python

I came across anthonywritescode’s Github repository for his twitch-chat-bot which is written in Python. I have not written much Python in my life so maybe this is trivial, but I found it to be a neat little trick anyways.

Consider you have the following JSON config file.

// file: config.json
{
    "username": "claw0ry",
    "token": "636DDA4D-A395-43C5-A2B1-7A0401DE51AB"

}

In the past I would probably have loaded it like this:

import json

class Config():
    username: str
    token: str

    def validate_username(self) -> bool:
        return True if len(self.username) > 0 else False

with open('./config.json') as f:
    d = json.load(f)
    cfg = Config(username=d.username, token=d.token)

print(cfg.validate_username())

What we essentially are doing is that we load the config.json into a variable as dictionary and then we initiate a new Config class and assign each class property by arguments. With this little trick we can make Python do it for us.

import json
from typing import NamedTuple

class Config(NamedTuple):
    username: str
    token: str

    def validate_username(self) -> bool:
        return True if len(self.username) > 0 else False

with open('./config.json') as f:
    cfg = Config(**json.load(f))

print(cfg.validate_username())

The first thing to notice is that our Config class now takes arguments in the form of a NamedTuple. Then we have combined the json.load() with ** when initiating our Config class. The json.load() method will give us a Python dictionary from the config.json file. We then unpack the dictionary (with **) into named arguments for the Config class.

It’s not much, but a neat little shortcut and in my opinion it reads a little better too.