1 files changed, 25 insertions, 18 deletions

diff --git a/natsort/compat/locale.py b/natsort/compat/locale.py
index ccb5592..9af5e7a 100644
--- a/natsort/compat/locale.py
+++ b/natsort/compat/locale.py
@@ -3,9 +3,11 @@
 Interface for natsort to access locale functionality without
 having to worry about if it is using PyICU or the built-in locale.
 """
-
-# Std. lib imports.
 import sys
+from typing import Callable, Union, cast
+
+StrOrBytes = Union[str, bytes]
+TrxfmFunc = Callable[[str], StrOrBytes]
 
 # This string should be sorted after any other byte string because
 # it contains the max unicode character repeated 20 times.
@@ -13,6 +15,11 @@ import sys
 null_string = ""
 null_string_max = chr(sys.maxunicode) * 20
 
+# This variable could be str or bytes depending on the locale library
+# being used, so give the type-checker this information.
+null_string_locale: StrOrBytes
+null_string_locale_max: StrOrBytes
+
 # strxfrm can be buggy (especially on BSD-based systems),
 # so prefer icu if available.
 try:  # noqa: C901
@@ -26,26 +33,26 @@ try:  # noqa: C901
     # You would need some odd data to come after that.
     null_string_locale_max = b"x7f" * 50
 
-    def dumb_sort():
+    def dumb_sort() -> bool:
         return False
 
     # If using icu, get the locale from the current global locale,
-    def get_icu_locale():
+    def get_icu_locale() -> str:
         try:
-            return icu.Locale(".".join(getlocale()))
+            return cast(str, icu.Locale(".".join(getlocale())))
         except TypeError:  # pragma: no cover
-            return icu.Locale()
+            return cast(str, icu.Locale())
 
-    def get_strxfrm():
-        return icu.Collator.createInstance(get_icu_locale()).getSortKey
+    def get_strxfrm() -> TrxfmFunc:
+        return cast(TrxfmFunc, icu.Collator.createInstance(get_icu_locale()).getSortKey)
 
-    def get_thousands_sep():
+    def get_thousands_sep() -> str:
         sep = icu.DecimalFormatSymbols.kGroupingSeparatorSymbol
-        return icu.DecimalFormatSymbols(get_icu_locale()).getSymbol(sep)
+        return cast(str, icu.DecimalFormatSymbols(get_icu_locale()).getSymbol(sep))
 
-    def get_decimal_point():
+    def get_decimal_point() -> str:
         sep = icu.DecimalFormatSymbols.kDecimalSeparatorSymbol
-        return icu.DecimalFormatSymbols(get_icu_locale()).getSymbol(sep)
+        return cast(str, icu.DecimalFormatSymbols(get_icu_locale()).getSymbol(sep))
 
 
 except ImportError:
@@ -57,14 +64,14 @@ except ImportError:
 
     # On some systems, locale is broken and does not sort in the expected
     # order. We will try to detect this and compensate.
-    def dumb_sort():
+    def dumb_sort() -> bool:
         return strxfrm("A") < strxfrm("a")
 
-    def get_strxfrm():
+    def get_strxfrm() -> TrxfmFunc:
         return strxfrm
 
-    def get_thousands_sep():
-        sep = locale.localeconv()["thousands_sep"]
+    def get_thousands_sep() -> str:
+        sep = cast(str, locale.localeconv()["thousands_sep"])
         # If this locale library is broken, some of the thousands separator
         # characters are incorrectly blank. Here is a lookup table of the
         # corrections I am aware of.
@@ -111,5 +118,5 @@ except ImportError:
         else:
             return sep
 
-    def get_decimal_point():
-        return locale.localeconv()["decimal_point"]
+    def get_decimal_point() -> str:
+        return cast(str, locale.localeconv()["decimal_point"])