[core] Simplify code for report_warning().

[mk-pmb]

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I think this way it's easier to read, and thus, easier to maintain.

[mk-pmb]

GitHub seems to not show me your question in the code view, so I have to reply here: I'm ok with the double low line prefix. If someone needs this method in another scope, they can PR it. I'll amend.

[dirkf]

Thanks for this.

There may be some weirdness in how things like report_warning() work because of back-porting yt-dlp changes to extractor/common.py and YoutubeDL.py separately. Also, there are overrides in the test code as well (eg, to turn off colours).

Overall, I think the best way to improve this is to have

1. a simplified version of utils.supports_terminal_sequences()
2. a YoutubeDL._format_err() method like that in yt-dlp, but self-contained
3. a YoutubeDL.Styles object that encodes the ANSI terminal sequences.

So:

class YoutubeDL(object):
    ...
    Styles = collections.NamedTuple('Styles', ('EMPHASIS', 'WARNING'))(
        # ESC[0;34m  ESC[0m     ESC[0;33m   ESC[0m  
        '\033[0;34m%s\033[0m', '\033[0;33m%s\033[0m')
    ...
    def _format_err(self, text, f, *args, **kwargs):
        # ignoring: fallback=None, *, test_encoding=False
        if self.params.get('no_color') is True or not supports_terminal_sequences(self._err_file):
            return text
        return f % text
    ...

These changes would yield a subset of the equivalent yt-dlp code, making it easier to keep our code and theirs in sync.

[dirkf]

Maybe:

Suggested change

	prefix = 'WARNING:'
	if self.can_use_color_codes(output_file=self._err_file):
	prefix = '\033[0;33m' + prefix + '\033[0m'
	prefix = (
	'\033[0;33m{0}\033[0m'
	if self.can_use_color_codes(output_file=self._err_file)
	else '{0}').format('WARNING:')

[mk-pmb]

This feels confusing to me. Why would you always call .format() when one of the branches is a guaranteed verbatim copy?

[dirkf]

This method only depends on the instance to provide the no_color param. One possibility is to make it a function in utils.py with the no_color test separate.

If it's going to be a method here as-is:

1. the same code pattern in InfoExtractor._search_regex() should be addressed (and also that this looks at sys.stderr instead of self._downloader._err_file, probably wrong)
2. if the method is going to be called there, the name should lose the __, contrary to my original suggestion.

yt-dlp has invented minicurses.py which abstracts all this (more than we need, I think), but also this useful utils function that we might acquire:

@functools.cache
def supports_terminal_sequences(stream):
    if compat_os_name == 'nt':
        if not WINDOWS_VT_MODE:
            return False
    elif not os.getenv('TERM'):
        return False
    try:
        return stream.isatty()
    except BaseException:
        return False

The cache decorator that isn't available in all our supported Pythons can be simulated (I have an implementation but the margin of this comment is too small to contain it). The noteworthy changes:

• WINDOWS_VT_MODE is introduced, default False, that can be enabled by a Windows API call for recent Windows (>= 10.0.10586) -- we can ignore that
• the TERM env var is tested, which we don't do, and perhaps should
• the isatty() call is protected, probably sensible.

[mk-pmb]

That exceeds my current available mental energy, so I have no opinion. If you need any changes on my side, I need dumber instructions, or you could probably edit it yourself. (The "Allow edits … by maintainers" is checked.)