[utils] Allow partial application for more functions (#11391)

Also adds the `trim_str` traversal helper

Authored by: bashonly, Grub4K

Co-authored-by: Simon Sawicki <contact@grub4k.xyz>

test/test_traversal.py

@@ -12,9 +12,10 @@ from yt_dlp.utils import (
     str_or_none,
 )
 from yt_dlp.utils.traversal import (
-    traverse_obj,
     require,
     subs_list_to_dict,
+    traverse_obj,
+    trim_str,
 )
 
 _TEST_DATA = {
@@ -495,6 +496,20 @@ class TestTraversalHelpers:
             {'url': 'https://example.com/subs/en2', 'ext': 'ext'},
         ]}, '`quality` key should sort subtitle list accordingly'
 
+    def test_trim_str(self):
+        with pytest.raises(TypeError):
+            trim_str('positional')
+
+        assert callable(trim_str(start='a'))
+        assert trim_str(start='ab')('abc') == 'c'
+        assert trim_str(end='bc')('abc') == 'a'
+        assert trim_str(start='a', end='c')('abc') == 'b'
+        assert trim_str(start='ab', end='c')('abc') == ''
+        assert trim_str(start='a', end='bc')('abc') == ''
+        assert trim_str(start='ab', end='bc')('abc') == ''
+        assert trim_str(start='abc', end='abc')('abc') == ''
+        assert trim_str(start='', end='')('abc') == 'abc'
+
 
 class TestDictGet:
     def test_dict_get(self):

test/test_utils.py

@@ -4,6 +4,7 @@
 import os
 import sys
 import unittest
+import unittest.mock
 import warnings
 import datetime as dt
 
@@ -71,6 +72,7 @@ from yt_dlp.utils import (
     intlist_to_bytes,
     iri_to_uri,
     is_html,
+    join_nonempty,
     js_to_json,
     limit_length,
     locked_file,
@@ -343,11 +345,13 @@ class TestUtil(unittest.TestCase):
         self.assertEqual(remove_start(None, 'A - '), None)
         self.assertEqual(remove_start('A - B', 'A - '), 'B')
         self.assertEqual(remove_start('B - A', 'A - '), 'B - A')
+        self.assertEqual(remove_start('non-empty', ''), 'non-empty')
 
     def test_remove_end(self):
         self.assertEqual(remove_end(None, ' - B'), None)
         self.assertEqual(remove_end('A - B', ' - B'), 'A')
         self.assertEqual(remove_end('B - A', ' - B'), 'B - A')
+        self.assertEqual(remove_end('non-empty', ''), 'non-empty')
 
     def test_remove_quotes(self):
         self.assertEqual(remove_quotes(None), None)
@@ -2148,6 +2152,16 @@ Line 1
             assert run_shell(args) == expected
             assert run_shell(shell_quote(args, shell=True)) == expected
 
+    def test_partial_application(self):
+        assert callable(int_or_none(scale=10)), 'missing positional parameter should apply partially'
+        assert int_or_none(10, scale=0.1) == 100, 'positionally passed argument should call function'
+        assert int_or_none(v=10) == 10, 'keyword passed positional should call function'
+        assert int_or_none(scale=0.1)(10) == 100, 'call after partial applicatino should call the function'
+
+        assert callable(join_nonempty(delim=', ')), 'varargs positional should apply partially'
+        assert callable(join_nonempty()), 'varargs positional should apply partially'
+        assert join_nonempty(None, delim=', ') == '', 'passed varargs should call the function'
+
 
 if __name__ == '__main__':
     unittest.main()