Add LocalizedValue.translate()

LocalizedValue.translate() behaves the exact same as the str(..) cast
works, with the exception that it returns None if there is no value
instead of an empty string. This makes it easier to implement custom
value classes on top of the LocalizedValue class.

Behavior for str(..) stays the same as it was.

localized_fields/value.py

@@ -1,5 +1,7 @@
 import collections
 
+from typing import Optional
+
 from django.conf import settings
 from django.utils import translation
 
@@ -98,10 +100,10 @@ class LocalizedValue(dict):
             for val in value:
                 self._interpret_value(val)
 
-    def __str__(self) -> str:
-        """Gets the value in the current language, or falls
-        back to the primary language if there's no value
-        in the current language."""
+    def translate(self) -> Optional[str]:
+        """Gets the value in the current language or falls
+        back to the next language if there's no value in the
+        current language."""
 
         fallbacks = getattr(settings, 'LOCALIZED_FIELDS_FALLBACKS', {})
 
@@ -112,9 +114,16 @@ class LocalizedValue(dict):
         for lang_code in languages:
             value = self.get(lang_code)
             if value:
-                return value or ''
+                return value or None
 
-        return ''
+        return None
+
+    def __str__(self) -> str:
+        """Gets the value in the current language or falls
+        back to the next language if there's no value in the
+        current language."""
+
+        return self.translate() or ''
 
     def __eq__(self, other):
         """Compares :paramref:self to :paramref:other for

tests/test_value.py

@@ -1,7 +1,7 @@
-from django.conf import settings
-from django.test import TestCase
-from django.utils import translation
 from django.db.models import F
+from django.conf import settings
+from django.utils import translation
+from django.test import TestCase, override_settings
 
 from localized_fields.value import LocalizedValue
 
@@ -90,18 +90,6 @@ class LocalizedValueTestCase(TestCase):
             assert localized_value.get(language) == value
             assert getattr(localized_value, language) == value
 
-    @staticmethod
-    def test_str():
-        """Tests whether the :see:LocalizedValue
-        class's __str__ works properly."""
-
-        keys = get_init_values()
-        localized_value = LocalizedValue(keys)
-
-        for language, value in keys.items():
-            translation.activate(language)
-            assert str(localized_value) == value
-
     @staticmethod
     def test_eq():
         """Tests whether the __eq__ operator
@@ -116,9 +104,21 @@ class LocalizedValueTestCase(TestCase):
         assert a != b
 
     @staticmethod
-    def test_str_fallback():
+    def test_translate():
         """Tests whether the :see:LocalizedValue
-        class's __str__'s fallback functionality
+        class's __str__ works properly."""
+
+        keys = get_init_values()
+        localized_value = LocalizedValue(keys)
+
+        for language, value in keys.items():
+            translation.activate(language)
+            assert localized_value.translate() == value
+
+    @staticmethod
+    def test_translate_fallback():
+        """Tests whether the :see:LocalizedValue
+        class's translate()'s fallback functionality
         works properly."""
 
         test_value = 'myvalue'
@@ -131,13 +131,13 @@ class LocalizedValueTestCase(TestCase):
 
         # make sure that, by default it returns
         # the value in the default language
-        assert str(localized_value) == test_value
+        assert localized_value.translate() == test_value
 
         # make sure that it falls back to the
         # primary language when there's no value
         # available in the current language
         translation.activate(other_language)
-        assert str(localized_value) == test_value
+        assert localized_value.translate() == test_value
 
         # make sure that it's just __str__ falling
         # back and that for the other language
@@ -145,12 +145,35 @@ class LocalizedValueTestCase(TestCase):
         assert localized_value.get(other_language) != test_value
 
     @staticmethod
-    def test_str_fallback_custom_fallback():
+    def test_translate_none():
+        """Tests whether the :see:LocalizedValue
+        class's translate() method properly returns
+        None when there is no value."""
+
+        # with no value, we always expect it to return None
+        localized_value = LocalizedValue()
+        assert localized_value.translate() == None
+        assert str(localized_value) == ''
+
+        # with no value for the default language, the default
+        # behavior is to return None, unless a custom fallback
+        # chain is configured, which there is not for this test
+        other_language = settings.LANGUAGES[-1][0]
+        localized_value = LocalizedValue({
+            other_language: 'hey'
+        })
+
+        translation.activate(settings.LANGUAGE_CODE)
+        assert localized_value.translate() == None
+        assert str(localized_value) == ''
+
+    @staticmethod
+    def test_translate_fallback_custom_fallback():
         """Tests whether the :see:LocalizedValue class's
-        __str__'s fallback functionality properly respects
+        translate()'s fallback functionality properly respects
         the LOCALIZED_FIELDS_FALLBACKS setting."""
 
-        settings.LOCALIZED_FIELDS_FALLBACKS = {
+        fallbacks = {
             'nl': ['ro']
         }
 
@@ -159,8 +182,9 @@ class LocalizedValueTestCase(TestCase):
             'ro': 'ro'
         })
 
+        with override_settings(LOCALIZED_FIELDS_FALLBACKS=fallbacks):
             with translation.override('nl'):
-            assert str(localized_value) == 'ro'
+                assert localized_value.translate() == 'ro'
 
     @staticmethod
     def test_deconstruct():