Explanation of code

[ejKDE]

Here's an example of the code. I'd like to know what ctx is here. It's not passed anywhere to a function and i can't use get('formats')[::-1] without this function. How does it work and called?

import yt_dlp

URLS = ['https://www.youtube.com/watch?v=BaW_jenozKc']

def format_selector(ctx):
    formats = ctx.get('formats')[::-1]

   .....


ydl_opts = {
    'format': format_selector,
}

with yt_dlp.YoutubeDL(ydl_opts) as ydl:
    ydl.download(URLS)

buran write Feb-26-2024, 12:09 PM:
Please, use python tags when post code

[Gribouillis]

Obviously the format_selector() function is called either by YoutubeDL(ydl_opts) or by ydl.download(URLS). The ctx argument is created internally by the yt_dlp module. You can find the type of this object and see where it is called by replacing the function by

def format_selector(ctx):
    raise RuntimeError(ctx)

[ejKDE]

Thank you. So if i understood correctly, YoutubeDL looks at ydl_opts, sees format in 'format': format_selector and is sending all of the format related things to format_selector function even though function is called without arguments?

This is specific to yt_dlp, right? I can't do this with my own functions, i need to send arguments or use *args.

[buran]

even though function is called without arguments?

You never call the function format_selector yourself, it's called internally from YoutubeDL.download and it expects that it takes ctx argument

From the docstring for YoutubeDL class

format: Video format code. see "FORMAT SELECTION" for more details.
You can also pass a function. The function takes 'ctx' as
argument and returns the formats to download

[ejKDE]

Ok, thank you!