[outtmpl] Format type `U` for unicode normalization

README.md

@@ -964,6 +964,7 @@ The field names themselves (the part inside the parenthesis) can also have some
 1. **Alternatives**: Alternate fields can be specified seperated with a `,`. Eg: `%(release_date>%Y,upload_date>%Y|Unknown)s`
 1. **Default**: A literal default value can be specified for when the field is empty using a `|` seperator. This overrides `--output-na-template`. Eg: `%(uploader|Unknown)s`
 1. **More Conversions**: In addition to the normal format types `diouxXeEfFgGcrs`, `B`, `j`, `l`, `q` can be used for converting to **B**ytes, **j**son, a comma seperated **l**ist and a string **q**uoted for the terminal respectively
+1. **Unicode normalization**: The format type `U` can be used for NFC [unicode normalization](https://docs.python.org/3/library/unicodedata.html#unicodedata.normalize). The alternate form flag (`#`) changes the normalization to NFD and the conversion flag `+` can be used for NFKC/NFKD compatibility equivalence normalization. Eg: `%(title)+.100U` is NFKC
 
 To summarize, the general syntax for a field is:
 ```

test/test_YoutubeDL.py

@@ -649,7 +649,7 @@ class TestYoutubeDL(unittest.TestCase):
         'title2': '%PATH%',
         'title3': 'foo/bar\\test',
         'title4': 'foo "bar" test',
-        'title5': 'áéí',
+        'title5': 'áéí 𝐀',
         'timestamp': 1618488000,
         'duration': 100000,
         'playlist_index': 1,
@@ -769,6 +769,10 @@ class TestYoutubeDL(unittest.TestCase):
         test('%(formats.:.id) 15l', '  id1, id2, id3')
         test('%(formats)j', (json.dumps(FORMATS), sanitize(json.dumps(FORMATS))))
         test('%(title5).3B', 'á')
+        test('%(title5)U', 'áéí 𝐀')
+        test('%(title5)#U', 'a\u0301e\u0301i\u0301 𝐀')
+        test('%(title5)+U', 'áéí A')
+        test('%(title5)+#U', 'a\u0301e\u0301i\u0301 A')
         if compat_os_name == 'nt':
             test('%(title4)q', ('"foo \\"bar\\" test"', "'foo _'bar_' test'"))
         else:

yt_dlp/YoutubeDL.py

@@ -25,6 +25,7 @@ import time
 import tokenize
 import traceback
 import random
+import unicodedata
 
 from string import ascii_letters
 
@@ -908,7 +909,7 @@ class YoutubeDL(object):
     def validate_outtmpl(cls, outtmpl):
         ''' @return None or Exception object '''
         outtmpl = re.sub(
-            STR_FORMAT_RE_TMPL.format('[^)]*', '[ljqB]'),
+            STR_FORMAT_RE_TMPL.format('[^)]*', '[ljqBU]'),
             lambda mobj: f'{mobj.group(0)[:-1]}s',
             cls._outtmpl_expandpath(outtmpl))
         try:
@@ -940,7 +941,7 @@ class YoutubeDL(object):
         }
 
         TMPL_DICT = {}
-        EXTERNAL_FORMAT_RE = re.compile(STR_FORMAT_RE_TMPL.format('[^)]*', f'[{STR_FORMAT_TYPES}ljqB]'))
+        EXTERNAL_FORMAT_RE = re.compile(STR_FORMAT_RE_TMPL.format('[^)]*', f'[{STR_FORMAT_TYPES}ljqBU]'))
         MATH_FUNCTIONS = {
             '+': float.__add__,
             '-': float.__sub__,
@@ -1031,21 +1032,26 @@ class YoutubeDL(object):
             value = default if value is None else value
 
             str_fmt = f'{fmt[:-1]}s'
-            if fmt[-1] == 'l':
+            if fmt[-1] == 'l':  # list
                 value, fmt = ', '.join(variadic(value)), str_fmt
-            elif fmt[-1] == 'j':
+            elif fmt[-1] == 'j':  # json
                 value, fmt = json.dumps(value, default=_dumpjson_default), str_fmt
-            elif fmt[-1] == 'q':
+            elif fmt[-1] == 'q':  # quoted
                 value, fmt = compat_shlex_quote(str(value)), str_fmt
-            elif fmt[-1] == 'B':
+            elif fmt[-1] == 'B':  # bytes
                 value = f'%{str_fmt}'.encode('utf-8') % str(value).encode('utf-8')
                 value, fmt = value.decode('utf-8', 'ignore'), 's'
+            elif fmt[-1] == 'U':  # unicode normalized
+                opts = outer_mobj.group('conversion') or ''
+                value, fmt = unicodedata.normalize(
+                    # "+" = compatibility equivalence, "#" = NFD
+                    'NF%s%s' % ('K' if '+' in opts else '', 'D' if '#' in opts else 'C'),
+                    value), str_fmt
             elif fmt[-1] == 'c':
-                value = str(value)
+                if value:
-                if value is None:
+                    value = str(value)[0]
-                    value, fmt = default, 's'
                 else:
-                    value = value[0]
+                    fmt = str_fmt
             elif fmt[-1] not in 'rs':  # numeric
                 value = float_or_none(value)
                 if value is None:

yt_dlp/utils.py

@@ -4474,12 +4474,12 @@ OUTTMPL_TYPES = {
 STR_FORMAT_RE_TMPL = r'''(?x)
     (?<!%)(?P<prefix>(?:%%)*)
     %
-    (?P<has_key>\((?P<key>{0})\))?  # mapping key
+    (?P<has_key>\((?P<key>{0})\))?
     (?P<format>
-        (?:[#0\-+ ]+)?  # conversion flags (optional)
+        (?P<conversion>[#0\-+ ]+)?
-        (?:\d+)?  # minimum field width (optional)
+        (?P<min_width>\d+)?
-        (?:\.\d+)?  # precision (optional)
+        (?P<precision>\.\d+)?
-        [hlL]?  # length modifier (optional)
+        (?P<len_mod>[hlL])?  # unused in python
         {1}  # conversion type
     )
 '''