Added a get_current_locale function, compliant with setlocale, to avoid misuses of getlocale (see pandas-dev#46595). Added tests.

Author: Sylvain MARIE

pandas/_config/localization.py

@@ -17,6 +17,29 @@
 from pandas._config.config import options
 
 
+def get_current_locale(lc_var: int = locale.LC_ALL):
+    """
+    Return the current locale associated with category ``lc_var``.
+    This is a convenience method to avoid misuses of ``getlocale``. Indeed the
+    result returned by ``getlocale`` can not always be used to set back the locale
+    using ``setlocale``. See GH#46595
+
+    Parameters
+    ----------
+    lc_var : int, default `locale.LC_ALL`
+        The category of the locale being set.
+
+    Returns
+    -------
+
+    """
+    # `getlocale` does not always play well with `setLocale`, avoid using it
+    # return locale.getlocale()
+
+    # Using `setlocale` with no second argument returns the current locale
+    return locale.setlocale(lc_var)
+
+
 @contextmanager
 def set_locale(
     new_locale: str | tuple[str, str], lc_var: int = locale.LC_ALL
@@ -39,8 +62,8 @@ def set_locale(
     particular locale, without globally setting the locale. This probably isn't
     thread-safe.
     """
-    # getlocale is wrong, see GH#46595
-    current_locale = locale.setlocale(lc_var)
+    # getlocale is not always compliant with setlocale, see GH#46595
+    current_locale = get_current_locale(lc_var=lc_var)
 
     try:
         locale.setlocale(lc_var, new_locale)

pandas/tests/config/test_localization.py

@@ -6,35 +6,74 @@
 
 from pandas._config.localization import (
     can_set_locale,
+    get_current_locale,
     get_locales,
     set_locale,
 )
 
-from pandas.compat import is_platform_windows
-
 import pandas as pd
 
 _all_locales = get_locales() or []
 _current_locale = locale.setlocale(locale.LC_ALL)  # getlocale() is wrong, see GH#46595
 
-# Don't run any of these tests if we are on Windows or have no locales.
-pytestmark = pytest.mark.skipif(
-    is_platform_windows() or not _all_locales, reason="Need non-Windows and locales"
-)
+# Don't run any of these tests if we have no locales.
+pytestmark = pytest.mark.skipif(not _all_locales, reason="Need locales")
 
 _skip_if_only_one_locale = pytest.mark.skipif(
     len(_all_locales) <= 1, reason="Need multiple locales for meaningful test"
 )
 
 
-def test_can_set_locale_valid_set():
+@pytest.mark.parametrize("lc_var", (locale.LC_ALL, locale.LC_CTYPE, locale.LC_TIME))
+def test_get_current_locale(lc_var):
+    # Make sure that `get_current_locale` uses setlocale
+    before_locale = get_current_locale(lc_var)
+    assert before_locale == locale.setlocale(lc_var)
+
+
+@pytest.mark.parametrize("lc_var", (locale.LC_ALL, locale.LC_CTYPE, locale.LC_TIME))
+def test_can_set_current_locale(lc_var):
+    # Can set the current locale
+    before_locale = get_current_locale(lc_var)
+    assert can_set_locale(before_locale, lc_var=lc_var)
+    after_locale = get_current_locale(lc_var)
+    assert before_locale == after_locale
+
+
+@pytest.mark.parametrize("lc_var", (locale.LC_ALL, locale.LC_CTYPE, locale.LC_TIME))
+def test_can_set_locale_valid_set(lc_var):
     # Can set the default locale.
-    assert can_set_locale("")
+    before_locale = get_current_locale(lc_var)
+    assert can_set_locale("", lc_var=lc_var)
+    after_locale = get_current_locale(lc_var)
+    assert before_locale == after_locale
 
 
-def test_can_set_locale_invalid_set():
+@pytest.mark.parametrize("lc_var", (locale.LC_ALL, locale.LC_CTYPE, locale.LC_TIME))
+def test_can_set_locale_invalid_set(lc_var):
     # Cannot set an invalid locale.
-    assert not can_set_locale("non-existent_locale")
+    before_locale = get_current_locale(lc_var)
+    assert not can_set_locale("non-existent_locale", lc_var=lc_var)
+    after_locale = get_current_locale(lc_var)
+    assert before_locale == after_locale
+
+
+@pytest.mark.parametrize(
+    "lang,enc",
+    [
+        ("it_CH", "UTF-8"),
+        ("en_US", "ascii"),
+        ("zh_CN", "GB2312"),
+        ("it_IT", "ISO-8859-1"),
+    ],
+)
+@pytest.mark.parametrize("lc_var", (locale.LC_ALL, locale.LC_CTYPE, locale.LC_TIME))
+def test_can_set_locale_no_leak(lang, enc, lc_var):
+    # Test that can_set_locale does not leak even when returning False. See GH#46595
+    before_locale = get_current_locale(lc_var)
+    can_set_locale((lang, enc), locale.LC_ALL)
+    after_locale = get_current_locale(lc_var)
+    assert before_locale == after_locale
 
 
 def test_can_set_locale_invalid_get(monkeypatch):