gh-91576: Speed up iteration of strings (#91574)

1 files changed, 31 insertions, 0 deletions

diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index df7afd5..c98fabf 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -9,6 +9,7 @@ import _string
 import codecs
 import itertools
 import operator
+import pickle
 import struct
 import sys
 import textwrap
@@ -185,6 +186,36 @@ class UnicodeTest(string_tests.CommonTest,
         self.assertEqual(next(it), "\u3333")
         self.assertRaises(StopIteration, next, it)
 
+    def test_iterators_invocation(self):
+        cases = [type(iter('abc')), type(iter('🚀'))]
+        for cls in cases:
+            with self.subTest(cls=cls):
+                self.assertRaises(TypeError, cls)
+
+    def test_iteration(self):
+        cases = ['abc', '🚀🚀🚀', "\u1111\u2222\u3333"]
+        for case in cases:
+            with self.subTest(string=case):
+                self.assertEqual(case, "".join(iter(case)))
+
+    def test_exhausted_iterator(self):
+        cases = ['abc', '🚀🚀🚀', "\u1111\u2222\u3333"]
+        for case in cases:
+            with self.subTest(case=case):
+                iterator = iter(case)
+                tuple(iterator)
+                self.assertRaises(StopIteration, next, iterator)
+
+    def test_pickle_iterator(self):
+        cases = ['abc', '🚀🚀🚀', "\u1111\u2222\u3333"]
+        for case in cases:
+            with self.subTest(case=case):
+                for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+                    it = iter(case)
+                    with self.subTest(proto=proto):
+                        pickled = "".join(pickle.loads(pickle.dumps(it, proto)))
+                        self.assertEqual(case, pickled)
+
     def test_count(self):
         string_tests.CommonTest.test_count(self)
         # check mixed argument types