Add TranslatedString class that handles KeyError during % substitution

src/tribler/gui/tests/test_utilities.py

@@ -3,7 +3,8 @@
 
 import pytest
 
-from tribler.gui.utilities import compose_magnetlink, create_api_key, dict_item_is_any_of, duration_to_string, \
+from tribler.gui.utilities import TranslatedString, compose_magnetlink, create_api_key, dict_item_is_any_of, \
+    duration_to_string, \
     format_api_key, \
     quote_plus_unicode, set_api_key, tr, unicode_quoter
 
@@ -175,7 +176,42 @@ def test_duration_to_string(seconds, translation):
     assert duration_to_string(seconds) == translation
 
 
-@patch('tribler.gui.utilities.QCoreApplication.translate', new=Mock(side_effect=KeyError('key is invalid')))
-def test_tr_exception():
-    # test if the tr function returns the key if the translation is not found
-    assert tr('0s') == '0s'
+def test_correct_translation():
+    original_string = 'original %(key1)s'
+    translated_string = 'translated %(key1)s'
+    s = TranslatedString(translated_string, original_string)
+    assert s % {'key1': '123'} == 'translated 123'
+
+
+@patch('tribler.gui.utilities.logger.warning')
+def test_missed_key_in_translated_string(warning: Mock):
+    original_string = 'original %(key1)s'
+    translated_string = 'translated %(key2)s'
+    s = TranslatedString(translated_string, original_string)
+
+    # In this test, we pass the correct param 'key1' presented in the original string but missed in the translation.
+    # The KeyError is intercepted, the original string is used instead of the translation, and the error is logged
+    # as a warning.
+    assert s % {'key1': '123'} == 'original 123'
+
+    warning.assert_called_once_with('KeyError: No value provided for \'key2\' in translation "translated %(key2)s", '
+                                    'original string: "original %(key1)s"')
+
+
+@patch('tribler.gui.utilities.logger.warning')
+def test_missed_key_in_both_translated_and_original_strings(warning: Mock):
+    original_string = 'original %(key1)s'
+    translated_string = 'translated %(key2)s'
+    s = TranslatedString(translated_string, original_string)
+
+    with pytest.raises(KeyError, match=r"^'key1'$"):
+        # In this test, we pass an incorrect param 'key3' for interpolation, and also, the translation
+        # string (with param 'key2') differs from the original string (with param 'key1'). First,
+        # translated string tries to interpolate params and issues a warning that 'key2' is missed.
+        # Then, the original string tries to interpolate params and again gets a KeyError because 'key1'
+        # is also missed. This second exception is propagated because the main reason for the error is
+        # in the outside code that passes an incorrect parameter.
+        s % {'key3': '123'}
+
+    warning.assert_called_once_with('KeyError: No value provided for \'key2\' in translation "translated %(key2)s", '
+                                    'original string: "original %(key1)s"')

src/tribler/gui/utilities.py

@@ -36,12 +36,26 @@
 NUM_VOTES_BARS = 8
 
 
+class TranslatedString(str):
+    def __new__(cls, translation, original_string):
+        return super().__new__(cls, translation)
+
+    def __init__(self, translation: str, original_string: str):  # pylint: disable=unused-argument
+        super().__init__()
+        self.original_string = original_string
+
+    def __mod__(self, other):
+        try:
+            return str.__mod__(self, other)
+        except KeyError as e:
+            msg = f'No value provided for {e} in translation "{self}", original string: "{self.original_string}"'
+            logger.warning(f'{type(e).__name__}: {msg}')
+            return self.original_string % other
+
+
 def tr(key):
-    try:
-        return str(QCoreApplication.translate('@default', key))
-    except KeyError as e:
-        logger.warning(f'{type(e).__name__}: {e} in "{key}"')
-        return key
+    translated_string = QCoreApplication.translate('@default', key)
+    return TranslatedString(translated_string, original_string=key)
 
 
 VOTES_RATING_DESCRIPTIONS = (