GH-101588: Deprecate pickle/copy/deepcopy support in itertools

Doc/whatsnew/3.12.rst

@@ -998,6 +998,12 @@ Pending Removal in Python 3.14
   functions that have been deprecated since Python 2 but only gained a
   proper :exc:`DeprecationWarning` in 3.12. Remove them in 3.14.
 
+* :mod:`itertools` had undocumented, inefficient, historically buggy,
+  and inconsistent support for copy, deepcopy, and pickle operations.
+  This will be removed in 3.14 with a significant reduction in code
+  volume and maintenance burden.
+  (Contributed by Raymond Hettinger in :gh:`101588`.)
+
 * Accessing ``co_lnotab`` was deprecated in :pep:`626` since 3.10
   and was planned to be removed in 3.12
   but it only got a proper :exc:`DeprecationWarning` in 3.12.

Lib/test/test_itertools.py

@@ -15,6 +15,20 @@
 import struct
 import threading
 import gc
+import warnings
+
+def pickle_deprecated(testfunc):
+    """ Run the test twice. On the first pass, verify that a
+    Deprecation Warning is raised.  On the second pass, run
+    normally but with DeprecationWarnings temporarily disabled.
+    """
+    def inner(self):
+        with self.assertWarns(DeprecationWarning):
+            testfunc(self)
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore", category=DeprecationWarning)
+            testfunc(self)
+    return inner
 
 maxsize = support.MAX_Py_ssize_t
 minsize = -maxsize-1
@@ -124,6 +138,7 @@ def expand(it, i=0):
             c = expand(compare[took:])
             self.assertEqual(a, c);
 
+    @pickle_deprecated
     def test_accumulate(self):
         self.assertEqual(list(accumulate(range(10))),               # one positional arg
                           [0, 1, 3, 6, 10, 15, 21, 28, 36, 45])
@@ -220,6 +235,7 @@ def test_chain_from_iterable(self):
         self.assertRaises(TypeError, list, chain.from_iterable([2, 3]))
         self.assertEqual(list(islice(chain.from_iterable(repeat(range(5))), 2)), [0, 1])
 
+    @pickle_deprecated
     def test_chain_reducible(self):
         for oper in [copy.deepcopy] + picklecopiers:
             it = chain('abc', 'def')
@@ -233,6 +249,7 @@ def test_chain_reducible(self):
         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
             self.pickletest(proto, chain('abc', 'def'), compare=list('abcdef'))
 
+    @pickle_deprecated
     def test_chain_setstate(self):
         self.assertRaises(TypeError, chain().__setstate__, ())
         self.assertRaises(TypeError, chain().__setstate__, [])
@@ -246,6 +263,7 @@ def test_chain_setstate(self):
         it.__setstate__((iter(['abc', 'def']), iter(['ghi'])))
         self.assertEqual(list(it), ['ghi', 'a', 'b', 'c', 'd', 'e', 'f'])
 
+    @pickle_deprecated
     def test_combinations(self):
         self.assertRaises(TypeError, combinations, 'abc')       # missing r argument
         self.assertRaises(TypeError, combinations, 'abc', 2, 1) # too many arguments
@@ -269,7 +287,6 @@ def test_combinations(self):
             self.assertEqual(list(op(testIntermediate)),
                              [(0,1,3), (0,2,3), (1,2,3)])
 
-
         def combinations1(iterable, r):
             'Pure python version shown in the docs'
             pool = tuple(iterable)
@@ -337,6 +354,7 @@ def test_combinations_tuple_reuse(self):
         self.assertEqual(len(set(map(id, combinations('abcde', 3)))), 1)
         self.assertNotEqual(len(set(map(id, list(combinations('abcde', 3))))), 1)
 
+    @pickle_deprecated
     def test_combinations_with_replacement(self):
         cwr = combinations_with_replacement
         self.assertRaises(TypeError, cwr, 'abc')       # missing r argument
@@ -425,6 +443,7 @@ def test_combinations_with_replacement_tuple_reuse(self):
         self.assertEqual(len(set(map(id, cwr('abcde', 3)))), 1)
         self.assertNotEqual(len(set(map(id, list(cwr('abcde', 3))))), 1)
 
+    @pickle_deprecated
     def test_permutations(self):
         self.assertRaises(TypeError, permutations)              # too few arguments
         self.assertRaises(TypeError, permutations, 'abc', 2, 1) # too many arguments
@@ -531,6 +550,7 @@ def test_combinatorics(self):
                 self.assertEqual(comb, list(filter(set(perm).__contains__, cwr)))     # comb: cwr that is a perm
                 self.assertEqual(comb, sorted(set(cwr) & set(perm)))            # comb: both a cwr and a perm
 
+    @pickle_deprecated
     def test_compress(self):
         self.assertEqual(list(compress(data='ABCDEF', selectors=[1,0,1,0,1,1])), list('ACEF'))
         self.assertEqual(list(compress('ABCDEF', [1,0,1,0,1,1])), list('ACEF'))
@@ -564,7 +584,7 @@ def test_compress(self):
                     next(testIntermediate)
                     self.assertEqual(list(op(testIntermediate)), list(result2))
 
-
+    @pickle_deprecated
     def test_count(self):
         self.assertEqual(lzip('abc',count()), [('a', 0), ('b', 1), ('c', 2)])
         self.assertEqual(lzip('abc',count(3)), [('a', 3), ('b', 4), ('c', 5)])
@@ -613,6 +633,7 @@ def test_count(self):
         #check proper internal error handling for large "step' sizes
         count(1, maxsize+5); sys.exc_info()
 
+    @pickle_deprecated
     def test_count_with_stride(self):
         self.assertEqual(lzip('abc',count(2,3)), [('a', 2), ('b', 5), ('c', 8)])
         self.assertEqual(lzip('abc',count(start=2,step=3)),
@@ -675,6 +696,7 @@ def test_cycle(self):
         self.assertRaises(TypeError, cycle, 5)
         self.assertEqual(list(islice(cycle(gen3()),10)), [0,1,2,0,1,2,0,1,2,0])
 
+    @pickle_deprecated
     def test_cycle_copy_pickle(self):
         # check copy, deepcopy, pickle
         c = cycle('abc')
@@ -711,6 +733,7 @@ def test_cycle_copy_pickle(self):
             d = pickle.loads(p)                  # rebuild the cycle object
             self.assertEqual(take(20, d), list('cdeabcdeabcdeabcdeab'))
 
+    @pickle_deprecated
     def test_cycle_unpickle_compat(self):
         testcases = [
             b'citertools\ncycle\n(c__builtin__\niter\n((lI1\naI2\naI3\natRI1\nbtR((lI1\naI0\ntb.',
@@ -742,6 +765,7 @@ def test_cycle_unpickle_compat(self):
             it = pickle.loads(t)
             self.assertEqual(take(10, it), [2, 3, 1, 2, 3, 1, 2, 3, 1, 2])
 
+    @pickle_deprecated
     def test_cycle_setstate(self):
         # Verify both modes for restoring state
 
@@ -778,6 +802,7 @@ def test_cycle_setstate(self):
         self.assertRaises(TypeError, cycle('').__setstate__, ())
         self.assertRaises(TypeError, cycle('').__setstate__, ([],))
 
+    @pickle_deprecated
     def test_groupby(self):
         # Check whether it accepts arguments correctly
         self.assertEqual([], list(groupby([])))
@@ -935,6 +960,7 @@ def test_filter(self):
             c = filter(isEven, range(6))
             self.pickletest(proto, c)
 
+    @pickle_deprecated
     def test_filterfalse(self):
         self.assertEqual(list(filterfalse(isEven, range(6))), [1,3,5])
         self.assertEqual(list(filterfalse(None, [0,1,0,2,0])), [0,0,0])
@@ -965,6 +991,7 @@ def test_zip(self):
                          lzip('abc', 'def'))
 
     @support.impl_detail("tuple reuse is specific to CPython")
+    @pickle_deprecated
     def test_zip_tuple_reuse(self):
         ids = list(map(id, zip('abc', 'def')))
         self.assertEqual(min(ids), max(ids))
@@ -1040,6 +1067,7 @@ def test_zip_longest_tuple_reuse(self):
         ids = list(map(id, list(zip_longest('abc', 'def'))))
         self.assertEqual(len(dict.fromkeys(ids)), len(ids))
 
+    @pickle_deprecated
     def test_zip_longest_pickling(self):
         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
             self.pickletest(proto, zip_longest("abc", "def"))
@@ -1186,6 +1214,7 @@ def test_product_tuple_reuse(self):
         self.assertEqual(len(set(map(id, product('abc', 'def')))), 1)
         self.assertNotEqual(len(set(map(id, list(product('abc', 'def'))))), 1)
 
+    @pickle_deprecated
     def test_product_pickling(self):
         # check copy, deepcopy, pickle
         for args, result in [
@@ -1201,6 +1230,7 @@ def test_product_pickling(self):
             for proto in range(pickle.HIGHEST_PROTOCOL + 1):
                 self.pickletest(proto, product(*args))
 
+    @pickle_deprecated
     def test_product_issue_25021(self):
         # test that indices are properly clamped to the length of the tuples
         p = product((1, 2),(3,))
@@ -1211,6 +1241,7 @@ def test_product_issue_25021(self):
         p.__setstate__((0, 0, 0x1000))  # will access tuple element 1 if not clamped
         self.assertRaises(StopIteration, next, p)
 
+    @pickle_deprecated
     def test_repeat(self):
         self.assertEqual(list(repeat(object='a', times=3)), ['a', 'a', 'a'])
         self.assertEqual(lzip(range(3),repeat('a')),
@@ -1243,6 +1274,7 @@ def test_repeat_with_negative_times(self):
         self.assertEqual(repr(repeat('a', times=-1)), "repeat('a', 0)")
         self.assertEqual(repr(repeat('a', times=-2)), "repeat('a', 0)")
 
+    @pickle_deprecated
     def test_map(self):
         self.assertEqual(list(map(operator.pow, range(3), range(1,7))),
                          [0**1, 1**2, 2**3])
@@ -1273,6 +1305,7 @@ def test_map(self):
             c = map(tupleize, 'abc', count())
             self.pickletest(proto, c)
 
+    @pickle_deprecated
     def test_starmap(self):
         self.assertEqual(list(starmap(operator.pow, zip(range(3), range(1,7)))),
                          [0**1, 1**2, 2**3])
@@ -1300,6 +1333,7 @@ def test_starmap(self):
             c = starmap(operator.pow, zip(range(3), range(1,7)))
             self.pickletest(proto, c)
 
+    @pickle_deprecated
     def test_islice(self):
         for args in [          # islice(args) should agree with range(args)
                 (10, 20, 3),
@@ -1394,6 +1428,7 @@ def __index__(self):
         self.assertEqual(list(islice(range(100), IntLike(10), IntLike(50), IntLike(5))),
                          list(range(10,50,5)))
 
+    @pickle_deprecated
     def test_takewhile(self):
         data = [1, 3, 5, 20, 2, 4, 6, 8]
         self.assertEqual(list(takewhile(underten, data)), [1, 3, 5])
@@ -1414,6 +1449,7 @@ def test_takewhile(self):
         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
             self.pickletest(proto, takewhile(underten, data))
 
+    @pickle_deprecated
     def test_dropwhile(self):
         data = [1, 3, 5, 20, 2, 4, 6, 8]
         self.assertEqual(list(dropwhile(underten, data)), [20, 2, 4, 6, 8])
@@ -1431,6 +1467,7 @@ def test_dropwhile(self):
         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
             self.pickletest(proto, dropwhile(underten, data))
 
+    @pickle_deprecated
     def test_tee(self):
         n = 200
 
@@ -1732,6 +1769,7 @@ class TestExamples(unittest.TestCase):
     def test_accumulate(self):
         self.assertEqual(list(accumulate([1,2,3,4,5])), [1, 3, 6, 10, 15])
 
+    @pickle_deprecated
     def test_accumulate_reducible(self):
         # check copy, deepcopy, pickle
         data = [1, 2, 3, 4, 5]
@@ -1747,6 +1785,7 @@ def test_accumulate_reducible(self):
         self.assertEqual(list(copy.deepcopy(it)), accumulated[1:])
         self.assertEqual(list(copy.copy(it)), accumulated[1:])
 
+    @pickle_deprecated
     def test_accumulate_reducible_none(self):
         # Issue #25718: total is None
         it = accumulate([None, None, None], operator.is_)

Misc/NEWS.d/next/Library/2023-05-26-01-31-30.gh-issue-101588.RaqxFy.rst

@@ -0,0 +1 @@
+Deprecate undocumented copy/deepcopy/pickle support for itertools.