[ie/youtube] Return empty playlist when channel/tab has no videos

Closes #8634

README.md

@@ -1268,7 +1268,7 @@ The field names themselves (the part inside the parenthesis) can also have some
 
 1. **Object traversal**: The dictionaries and lists available in metadata can be traversed by using a dot `.` separator; e.g. `%(tags.0)s`, `%(subtitles.en.-1.ext)s`. You can do Python slicing with colon `:`; E.g. `%(id.3:7:-1)s`, `%(formats.:.format_id)s`. Curly braces `{}` can be used to build dictionaries with only specific keys; e.g. `%(formats.:.{format_id,height})#j`. An empty field name `%()s` refers to the entire infodict; e.g. `%(.{id,title})s`. Note that all the fields that become available using this method are not listed below. Use `-j` to see such fields
 
-1. **Addition**: Addition and subtraction of numeric fields can be done using `+` and `-` respectively. E.g. `%(playlist_index+10)03d`, `%(n_entries+1-playlist_index)d`
+1. **Arithmetic**: Simple arithmetic can be done on numeric fields using `+`, `-` and `*`. E.g. `%(playlist_index+10)03d`, `%(n_entries+1-playlist_index)d`
 
 1. **Date/time Formatting**: Date/time fields can be formatted according to [strftime formatting](https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes) by specifying it separated from the field name using a `>`. E.g. `%(duration>%H-%M-%S)s`, `%(upload_date>%Y-%m-%d)s`, `%(epoch-3600>%H-%M-%S)s`
 

test/test_YoutubeDL.py

@@ -797,6 +797,7 @@ class TestYoutubeDL(unittest.TestCase):
         test('%(title|%)s %(title|%%)s', '% %%')
         test('%(id+1-height+3)05d', '00158')
         test('%(width+100)05d', 'NA')
+        test('%(filesize*8)d', '8192')
         test('%(formats.0) 15s', ('% 15s' % FORMATS[0], None))
         test('%(formats.0)r', (repr(FORMATS[0]), None))
         test('%(height.0)03d', '001')

yt_dlp/YoutubeDL.py

@@ -1179,6 +1179,7 @@ class YoutubeDL:
         MATH_FUNCTIONS = {
             '+': float.__add__,
             '-': float.__sub__,
+            '*': float.__mul__,
         }
         # Field is of the form key1.key2...
         # where keys (except first) can be string, int, slice or "{field, ...}"

yt_dlp/extractor/youtube.py

@@ -6469,6 +6469,9 @@ class YoutubeTabIE(YoutubeTabBaseInfoExtractor):
     def _has_tab(self, tabs, tab_id):
         return any(self._extract_tab_id_and_name(tab)[0] == tab_id for tab in tabs)
 
+    def _empty_playlist(self, item_id, data):
+        return self.playlist_result([], item_id, **self._extract_metadata_from_tabs(item_id, data))
+
     @YoutubeTabBaseInfoExtractor.passthrough_smuggled_data
     def _real_extract(self, url, smuggled_data):
         item_id = self._match_id(url)
@@ -6534,6 +6537,10 @@ class YoutubeTabIE(YoutubeTabBaseInfoExtractor):
             selected_tab_id, selected_tab_name = self._extract_tab_id_and_name(selected_tab, url)  # NB: Name may be translated
             self.write_debug(f'Selected tab: {selected_tab_id!r} ({selected_tab_name}), Requested tab: {original_tab_id!r}')
 
+            # /about is no longer a tab
+            if original_tab_id == 'about':
+                return self._empty_playlist(item_id, data)
+
             if not original_tab_id and selected_tab_name:
                 self.to_screen('Downloading all uploads of the channel. '
                                'To download only the videos in a specific tab, pass the tab\'s URL')
@@ -6546,7 +6553,7 @@ class YoutubeTabIE(YoutubeTabBaseInfoExtractor):
                 if not extra_tabs and selected_tab_id != 'videos':
                     # Channel does not have streams, shorts or videos tabs
                     if item_id[:2] != 'UC':
-                        raise ExtractorError('This channel has no uploads', expected=True)
+                        return self._empty_playlist(item_id, data)
 
                     # Topic channels don't have /videos. Use the equivalent playlist instead
                     pl_id = f'UU{item_id[2:]}'
@@ -6554,7 +6561,7 @@ class YoutubeTabIE(YoutubeTabBaseInfoExtractor):
                     try:
                         data, ytcfg = self._extract_data(pl_url, pl_id, ytcfg=ytcfg, fatal=True, webpage_fatal=True)
                     except ExtractorError:
-                        raise ExtractorError('This channel has no uploads', expected=True)
+                        return self._empty_playlist(item_id, data)
                     else:
                         item_id, url = pl_id, pl_url
                         self.to_screen(