How to use *args or **kwargs in f-strings?

Question

For example, I need *missing_vars to be an f-string in this logging. Because for logging.critical() one msg argument is needed, so I can't do this:

logging.critical(f'Required environment variables are missing: {*missing_vars}')

I can do it without *args, but I need it for a beautiful output, because it turns out like this:

>>> logging.critical(f'Required environment variables are missing: {missing_vars}')
Required environment variables are missing: ['PRACTICUM_TOKEN', 'TELEGRAM_TOKEN']`

But, I want like this:

Required environment variables are missing: PRACTICUM_TOKEN, TELEGRAM_TOKEN

My function:

def check_tokens():
    """Checks the availability of environment variables."""
    ENV_VARS = {
        'PRACTICUM_TOKEN': PRACTICUM_TOKEN,
        'TELEGRAM_TOKEN': TELEGRAM_TOKEN,
        'TELEGRAM_CHAT_ID': TELEGRAM_CHAT_ID,
    }
    missing_vars = [var for var, value in ENV_VARS.items() if not value]
    if missing_vars:
        logging.critical(f'Required environment variables are missing: {*missing_vars}') # <--
    else:
        return True

`{*missing_vars}` doesn't work because a starred expression is not allowed in this context. `logging.critical` would have still got a single string argument — DeepSpace, Aug 21 '22 at 10:14
then how do I get the beautiful output that I gave in the example? — finegorko, Aug 21 '22 at 10:16
Using the code provided in the first context. You map each item to its representation then join each value together separated by a comma and a space — Miguel Guthridge, Aug 21 '22 at 10:18
Change `repr` to `str` or use `", ".join(missing_vars)` directly if all elements of `missing_vars` are strings. — Mechanic Pig, Aug 21 '22 at 10:25
thank you! output now is `CRITICAL:root:Required environment variables are missing: PRACTICUM_TOKEN, TELEGRAM_TOKEN, TELEGRAM_CHAT_ID` Now I'm wondering if my code can be shortened? Does it happen in practice that I declare message for `missing_vars` separately `from logging.critical()`. [check_tokens()](https://i.imgur.com/7NWDokT.png) — finegorko, Aug 21 '22 at 10:28

finegorko · Accepted Answer · 2022-08-21T10:48:59.667

According to the comments of Mechanic Pig, I have updated my function and the output I need now, thank you!

def check_tokens():
    """Checks the availability of environment variables."""
    ENV_VARS = {
        'PRACTICUM_TOKEN': PRACTICUM_TOKEN,
        'TELEGRAM_TOKEN': TELEGRAM_TOKEN,
        'TELEGRAM_CHAT_ID': TELEGRAM_CHAT_ID,
    }
    missing_vars = [var for var, value in ENV_VARS.items() if not value]
    if missing_vars:
        logging.critical(
            f'Required environment variables are missing: '
            f'{", ".join(missing_vars)}'
        )
    else:
        return True

Output:

CRITICAL:root:Required environment variables are missing: PRACTICUM_TOKEN, TELEGRAM_TOKEN, TELEGRAM_CHAT_ID

How to use *args or **kwargs in f-strings?

1 Answers1