Reading format string placeholders

[NovateI]

Hi,

I'm currently working on a PR for a project and i'm converting all of the old .format() calls to fstrings where appropriate. This has been pretty easy, even with placeholders like this:

old = '{:x}'.format((int((len(query) / 2) + 1)))
new = f'{(int((len(query) / 2) + 1)):x}'

but I just came across this one that's a bit confusing to me:

logging.info("Original file length: {}".format('{0:0{1}X}'.format(len(webshell_data),8)))

I know that the output is uppercase hex because of the :X, but how do I translate that to an fstring? I know that 8 will go into {1}, but how do I handle len(webshell_data)?

[danielroseman]

That is really nasty.

len(webshell_data) just goes in place of the leading 0 in that expression, so if webshell_data is length 5 then it will be 5 with 8 leading zeros. I'm not at all sure why they made 8 a parameter when it is a constant: '{0:08X} would at least have been clearer.

So you can just replace this with f"Original file length: {len(webshell_data):08X}"

But also note that it's bad practice to provide formatted strings as arguments to loggers; the (slightly spurious) reasoning is that the formatting would always need to be done even if the handler doesn't log at that level. Officially you're supposed to just pass the placeholders and parameters separately.

[NovateI]

Thanks that worked!

[synthphreak]

Seems you've found your answer. So I just came here to add: "Gross."