add BabelTowerError

CHANGELOG.md

@@ -8,7 +8,7 @@
 + Add module `calendar` with `want_*` date type conversion utilities and `age_and_days()`
 + Move obsolete stuff to `obsolete` package (includes configparse 0.3 as of now)
 + Add `redact` module with `redact_url_password()`
-+ Add more exceptions: `NotFoundError()`
++ Add more exceptions: `NotFoundError()`, `BabelTowerError()`
 
 ## 0.4.0
 

src/suou/exceptions.py

@@ -45,6 +45,13 @@ class NotFoundError(LookupError):
     """
     The requested item was not found.
     """
+    # Werkzeug et al.
+    code = 404
+
+class BabelTowerError(NotFoundError):
+    """
+    The user requested a language that cannot be understood.
+    """
 
 __all__ = (
     'MissingConfigError', 'MissingConfigWarning', 'LexError', 'InconsistencyError', 'NotFoundError'

src/suou/i18n.py

@@ -23,6 +23,7 @@ import os
 import toml
 from typing import Mapping
 
+from .exceptions import BabelTowerError
 
 class IdentityLang:
     '''
@@ -81,7 +82,10 @@ class I18n(metaclass=ABCMeta):
     def load_lang(self, name: str, filename: str | None = None) -> I18nLang:
         if not filename:
             filename = self.filename_tmpl.format(lang=name, ext=self.EXT)
-        data = self.load_file(filename)
+        try:
+            data = self.load_file(filename)
+        except OSError as e:
+            raise BabelTowerError(f'unknown language: {name}') from e
         l = self.langs.setdefault(name, I18nLang())
         l.update(data[name] if name in data else data)
         if name != self.default_lang: