From 6941e32dbb9114109e935ab190115ca6d47c9a27 Mon Sep 17 00:00:00 2001
From: Isac Byeonghoon Yoo <isac.yoo@buzzvil.com>
Date: Thu, 8 Apr 2021 13:48:27 +0900
Subject: [PATCH] Utilize __init_subclass__ instead of inspect on Locale
 mapping to improve type checking (#920)

* Utilize __init_subclass__

* Add Unit Test for duplicated locale name

Co-authored-by: Jad Chaar <jad.chaar@gmail.com>
---
 arrow/locales.py      | 28 +++++++++++-----------------
 tests/conftest.py     |  2 +-
 tests/test_locales.py | 10 ++++++++--
 3 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/arrow/locales.py b/arrow/locales.py
index 8ceba33e2..90ca2b5c7 100644
--- a/arrow/locales.py
+++ b/arrow/locales.py
@@ -1,4 +1,3 @@
-import inspect
 import sys
 from math import trunc
 from typing import (
@@ -48,6 +47,9 @@
 ]
 
 
+_locale_map: Dict[str, Type["Locale"]] = dict()
+
+
 def get_locale(name: str) -> "Locale":
     """Returns an appropriate :class:`Locale <arrow.locales.Locale>`
     corresponding to an input locale name.
@@ -56,7 +58,7 @@ def get_locale(name: str) -> "Locale":
 
     """
 
-    locale_cls = _locales.get(name.lower())
+    locale_cls = _locale_map.get(name.lower())
 
     if locale_cls is None:
         raise ValueError(f"Unsupported locale {name!r}.")
@@ -121,6 +123,13 @@ class Locale:
 
     _month_name_to_ordinal: Optional[Dict[str, int]]
 
+    def __init_subclass__(cls, **kwargs: Any) -> None:
+        for locale_name in cls.names:
+            if locale_name in _locale_map:
+                raise LookupError(f"Duplicated locale name: {locale_name}")
+
+            _locale_map[locale_name] = cls
+
     def __init__(self) -> None:
 
         self._month_name_to_ordinal = None
@@ -3409,18 +3418,6 @@ class MarathiLocale(Locale):
     day_abbreviations = ["", "सोम", "मंगळ", "बुध", "गुरु", "शुक्र", "शनि", "रवि"]
 
 
-def _map_locales() -> Dict[str, Type[Locale]]:
-
-    locales: Dict[str, Type[Locale]] = {}
-
-    for _, cls in inspect.getmembers(sys.modules[__name__], inspect.isclass):
-        if issubclass(cls, Locale):  # pragma: no branch
-            for name in cls.names:
-                locales[name.lower()] = cls
-
-    return locales
-
-
 class CatalanLocale(Locale):
     names = ["ca", "ca_es", "ca_ad", "ca_fr", "ca_it"]
     past = "Fa {0}"
@@ -4644,6 +4641,3 @@ class LithuanianLocale(Locale):
         "še",
         "se",
     ]
-
-
-_locales: Dict[str, Type[Locale]] = _map_locales()
diff --git a/tests/conftest.py b/tests/conftest.py
index 4043bc3b1..5d5b9980e 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -49,7 +49,7 @@ def arrow_factory(request):
 
 @pytest.fixture(scope="class")
 def lang_locales(request):
-    request.cls.locales = locales._locales
+    request.cls.locales = locales._locale_map
 
 
 @pytest.fixture(scope="class")
diff --git a/tests/test_locales.py b/tests/test_locales.py
index 721d22bb1..6c984ecd6 100644
--- a/tests/test_locales.py
+++ b/tests/test_locales.py
@@ -33,6 +33,12 @@ def test_locale_validation(self):
             assert locale_cls.past is not None
             assert locale_cls.future is not None
 
+    def test_duplicated_locale_name(self):
+        with pytest.raises(LookupError):
+
+            class Locale1(locales.Locale):
+                names = ["en_us"]
+
 
 class TestModule:
     def test_get_locale(self, mocker):
@@ -43,7 +49,7 @@ def test_get_locale(self, mocker):
         with pytest.raises(ValueError):
             arrow.locales.get_locale("locale_name")
 
-        cls_dict = arrow.locales._locales
+        cls_dict = arrow.locales._locale_map
         mocker.patch.dict(cls_dict, {"locale_name": mock_locale_cls})
 
         result = arrow.locales.get_locale("locale_name")
@@ -68,7 +74,7 @@ def test_get_locale_by_class_name(self, mocker):
 
     def test_locales(self):
 
-        assert len(locales._locales) > 0
+        assert len(locales._locale_map) > 0
 
 
 @pytest.mark.usefixtures("lang_locale")