python · vstinner · Aug 14, 2019 · Jul 30, 2019 · Jul 31, 2019 · Aug 1, 2019
diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
@@ -1763,9 +1763,13 @@ expression support in the :mod:`re` module).
 .. method:: str.isspace()

   Return true if there are only whitespace characters in the string and there is
-   at least one character, false otherwise.  Whitespace characters  are those
-   characters defined in the Unicode character database as "Other" or "Separator"
-   and those with bidirectional property being one of "WS", "B", or "S".
+   at least one character, false otherwise.
+
+   A character is *whitespace* if in the Unicode character database
+   (see :mod:`unicodedata`), either its general category is ``Zs``
+   ("Separator, space"), or its bidirectional class is one of ``WS``,
+   ``B``, or ``S``.
+

 .. method:: str.istitle()


diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
@@ -12,6 +12,7 @@
 import struct
 import sys
 import textwrap
+import unicodedata
 import unittest
 import warnings
 from test import support, string_tests
@@ -617,11 +618,21 @@ def test_isspace(self):
        self.checkequalnofix(True, '\u2000', 'isspace')
        self.checkequalnofix(True, '\u200a', 'isspace')
        self.checkequalnofix(False, '\u2014', 'isspace')
-        # apparently there are no non-BMP spaces chars in Unicode 6
+        # There are no non-BMP whitespace chars as of Unicode 12.
        for ch in ['\U00010401', '\U00010427', '\U00010429', '\U0001044E',
                   '\U0001F40D', '\U0001F46F']:
            self.assertFalse(ch.isspace(), '{!a} is not space.'.format(ch))

+    @support.requires_resource('cpu')
+    def test_isspace_invariant(self):
+        for codepoint in range(sys.maxunicode + 1):
+            char = chr(codepoint)
+            bidirectional = unicodedata.bidirectional(char)
+            category = unicodedata.category(char)
+            self.assertEqual(char.isspace(),
+                             (bidirectional in ('WS', 'B', 'S')
+                              or category == 'Zs'))
+
    def test_isalnum(self):
        super().test_isalnum()
        for ch in ['\U00010401', '\U00010427', '\U00010429', '\U0001044E',