From 909c6f718913e713c990d69e6d8a74c05f81e2c2 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Wed, 25 Sep 2024 13:38:05 -0700 Subject: [PATCH] gh-123884 Tee of tee was not producing n independent iterators (gh-124490) --- Doc/library/itertools.rst | 45 ++++++---- .../pycore_global_objects_fini_generated.h | 1 - Include/internal/pycore_global_strings.h | 1 - .../internal/pycore_runtime_init_generated.h | 1 - .../internal/pycore_unicodeobject_generated.h | 4 - Lib/test/test_itertools.py | 84 +++++++++++-------- ...-09-24-22-38-51.gh-issue-123884.iEPTK4.rst | 4 + Modules/itertoolsmodule.c | 36 ++------ 8 files changed, 89 insertions(+), 87 deletions(-) create mode 100644 Misc/NEWS.d/next/Library/2024-09-24-22-38-51.gh-issue-123884.iEPTK4.rst diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst index 508c20f4df6..c1299ebfe8d 100644 --- a/Doc/library/itertools.rst +++ b/Doc/library/itertools.rst @@ -691,25 +691,36 @@ loops that truncate the stream. def tee(iterable, n=2): if n < 0: - raise ValueError('n must be >= 0') - iterator = iter(iterable) - shared_link = [None, None] - return tuple(_tee(iterator, shared_link) for _ in range(n)) + raise ValueError + if n == 0: + return () + iterator = _tee(iterable) + result = [iterator] + for _ in range(n - 1): + result.append(_tee(iterator)) + return tuple(result) - def _tee(iterator, link): - try: - while True: - if link[1] is None: - link[0] = next(iterator) - link[1] = [None, None] - value, link = link - yield value - except StopIteration: - return + class _tee: - Once a :func:`tee` has been created, the original *iterable* should not be - used anywhere else; otherwise, the *iterable* could get advanced without - the tee objects being informed. + def __init__(self, iterable): + it = iter(iterable) + if isinstance(it, _tee): + self.iterator = it.iterator + self.link = it.link + else: + self.iterator = it + self.link = [None, None] + + def __iter__(self): + return self + + def __next__(self): + link = self.link + if link[1] is None: + link[0] = next(self.iterator) + link[1] = [None, None] + value, self.link = link + return value When the input *iterable* is already a tee iterator object, all members of the return tuple are constructed as if they had been diff --git a/Include/internal/pycore_global_objects_fini_generated.h b/Include/internal/pycore_global_objects_fini_generated.h index 6e948e16b7d..a5f13692c62 100644 --- a/Include/internal/pycore_global_objects_fini_generated.h +++ b/Include/internal/pycore_global_objects_fini_generated.h @@ -604,7 +604,6 @@ _PyStaticObjects_CheckRefcnt(PyInterpreterState *interp) { _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__classdictcell__)); _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__complex__)); _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__contains__)); - _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__copy__)); _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__ctypes_from_outparam__)); _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__del__)); _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__delattr__)); diff --git a/Include/internal/pycore_global_strings.h b/Include/internal/pycore_global_strings.h index 5c63a6e519b..dd958dcd9fe 100644 --- a/Include/internal/pycore_global_strings.h +++ b/Include/internal/pycore_global_strings.h @@ -93,7 +93,6 @@ struct _Py_global_strings { STRUCT_FOR_ID(__classdictcell__) STRUCT_FOR_ID(__complex__) STRUCT_FOR_ID(__contains__) - STRUCT_FOR_ID(__copy__) STRUCT_FOR_ID(__ctypes_from_outparam__) STRUCT_FOR_ID(__del__) STRUCT_FOR_ID(__delattr__) diff --git a/Include/internal/pycore_runtime_init_generated.h b/Include/internal/pycore_runtime_init_generated.h index bac6b5b8fcf..8d7da8befc9 100644 --- a/Include/internal/pycore_runtime_init_generated.h +++ b/Include/internal/pycore_runtime_init_generated.h @@ -602,7 +602,6 @@ extern "C" { INIT_ID(__classdictcell__), \ INIT_ID(__complex__), \ INIT_ID(__contains__), \ - INIT_ID(__copy__), \ INIT_ID(__ctypes_from_outparam__), \ INIT_ID(__del__), \ INIT_ID(__delattr__), \ diff --git a/Include/internal/pycore_unicodeobject_generated.h b/Include/internal/pycore_unicodeobject_generated.h index efdbde4c8ea..d5ad61d4c62 100644 --- a/Include/internal/pycore_unicodeobject_generated.h +++ b/Include/internal/pycore_unicodeobject_generated.h @@ -172,10 +172,6 @@ _PyUnicode_InitStaticStrings(PyInterpreterState *interp) { _PyUnicode_InternStatic(interp, &string); assert(_PyUnicode_CheckConsistency(string, 1)); assert(PyUnicode_GET_LENGTH(string) != 1); - string = &_Py_ID(__copy__); - _PyUnicode_InternStatic(interp, &string); - assert(_PyUnicode_CheckConsistency(string, 1)); - assert(PyUnicode_GET_LENGTH(string) != 1); string = &_Py_ID(__ctypes_from_outparam__); _PyUnicode_InternStatic(interp, &string); assert(_PyUnicode_CheckConsistency(string, 1)); diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py index 6820dce3f12..8469de998ba 100644 --- a/Lib/test/test_itertools.py +++ b/Lib/test/test_itertools.py @@ -1249,10 +1249,11 @@ class TestBasicOps(unittest.TestCase): self.assertEqual(len(result), n) self.assertEqual([list(x) for x in result], [list('abc')]*n) - # tee pass-through to copyable iterator + # tee objects are independent (see bug gh-123884) a, b = tee('abc') c, d = tee(a) - self.assertTrue(a is c) + e, f = tee(c) + self.assertTrue(len({a, b, c, d, e, f}) == 6) # test tee_new t1, t2 = tee('abc') @@ -1759,21 +1760,36 @@ class TestPurePythonRoughEquivalents(unittest.TestCase): def tee(iterable, n=2): if n < 0: - raise ValueError('n must be >= 0') - iterator = iter(iterable) - shared_link = [None, None] - return tuple(_tee(iterator, shared_link) for _ in range(n)) + raise ValueError + if n == 0: + return () + iterator = _tee(iterable) + result = [iterator] + for _ in range(n - 1): + result.append(_tee(iterator)) + return tuple(result) - def _tee(iterator, link): - try: - while True: - if link[1] is None: - link[0] = next(iterator) - link[1] = [None, None] - value, link = link - yield value - except StopIteration: - return + class _tee: + + def __init__(self, iterable): + it = iter(iterable) + if isinstance(it, _tee): + self.iterator = it.iterator + self.link = it.link + else: + self.iterator = it + self.link = [None, None] + + def __iter__(self): + return self + + def __next__(self): + link = self.link + if link[1] is None: + link[0] = next(self.iterator) + link[1] = [None, None] + value, self.link = link + return value # End tee() recipe ############################################# @@ -1819,12 +1835,10 @@ class TestPurePythonRoughEquivalents(unittest.TestCase): self.assertRaises(TypeError, tee, [1,2], 'x') self.assertRaises(TypeError, tee, [1,2], 3, 'x') - # Tests not applicable to the tee() recipe - if False: - # tee object should be instantiable - a, b = tee('abc') - c = type(a)('def') - self.assertEqual(list(c), list('def')) + # tee object should be instantiable + a, b = tee('abc') + c = type(a)('def') + self.assertEqual(list(c), list('def')) # test long-lagged and multi-way split a, b, c = tee(range(2000), 3) @@ -1845,21 +1859,19 @@ class TestPurePythonRoughEquivalents(unittest.TestCase): self.assertEqual(len(result), n) self.assertEqual([list(x) for x in result], [list('abc')]*n) + # tee objects are independent (see bug gh-123884) + a, b = tee('abc') + c, d = tee(a) + e, f = tee(c) + self.assertTrue(len({a, b, c, d, e, f}) == 6) - # Tests not applicable to the tee() recipe - if False: - # tee pass-through to copyable iterator - a, b = tee('abc') - c, d = tee(a) - self.assertTrue(a is c) - - # test tee_new - t1, t2 = tee('abc') - tnew = type(t1) - self.assertRaises(TypeError, tnew) - self.assertRaises(TypeError, tnew, 10) - t3 = tnew(t1) - self.assertTrue(list(t1) == list(t2) == list(t3) == list('abc')) + # test tee_new + t1, t2 = tee('abc') + tnew = type(t1) + self.assertRaises(TypeError, tnew) + self.assertRaises(TypeError, tnew, 10) + t3 = tnew(t1) + self.assertTrue(list(t1) == list(t2) == list(t3) == list('abc')) # test that tee objects are weak referencable a, b = tee(range(10)) diff --git a/Misc/NEWS.d/next/Library/2024-09-24-22-38-51.gh-issue-123884.iEPTK4.rst b/Misc/NEWS.d/next/Library/2024-09-24-22-38-51.gh-issue-123884.iEPTK4.rst new file mode 100644 index 00000000000..55f1d4b4112 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2024-09-24-22-38-51.gh-issue-123884.iEPTK4.rst @@ -0,0 +1,4 @@ +Fixed bug in itertools.tee() handling of other tee inputs (a tee in a tee). +The output now has the promised *n* independent new iterators. Formerly, +the first iterator was identical (not independent) to the input iterator. +This would sometimes give surprising results. diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c index e740ec4d762..1201fa09490 100644 --- a/Modules/itertoolsmodule.c +++ b/Modules/itertoolsmodule.c @@ -1036,7 +1036,7 @@ itertools_tee_impl(PyObject *module, PyObject *iterable, Py_ssize_t n) /*[clinic end generated code: output=1c64519cd859c2f0 input=c99a1472c425d66d]*/ { Py_ssize_t i; - PyObject *it, *copyable, *copyfunc, *result; + PyObject *it, *to, *result; if (n < 0) { PyErr_SetString(PyExc_ValueError, "n must be >= 0"); @@ -1053,41 +1053,23 @@ itertools_tee_impl(PyObject *module, PyObject *iterable, Py_ssize_t n) return NULL; } - if (PyObject_GetOptionalAttr(it, &_Py_ID(__copy__), ©func) < 0) { - Py_DECREF(it); + itertools_state *state = get_module_state(module); + to = tee_fromiterable(state, it); + Py_DECREF(it); + if (to == NULL) { Py_DECREF(result); return NULL; } - if (copyfunc != NULL) { - copyable = it; - } - else { - itertools_state *state = get_module_state(module); - copyable = tee_fromiterable(state, it); - Py_DECREF(it); - if (copyable == NULL) { - Py_DECREF(result); - return NULL; - } - copyfunc = PyObject_GetAttr(copyable, &_Py_ID(__copy__)); - if (copyfunc == NULL) { - Py_DECREF(copyable); - Py_DECREF(result); - return NULL; - } - } - PyTuple_SET_ITEM(result, 0, copyable); + PyTuple_SET_ITEM(result, 0, to); for (i = 1; i < n; i++) { - copyable = _PyObject_CallNoArgs(copyfunc); - if (copyable == NULL) { - Py_DECREF(copyfunc); + to = tee_copy((teeobject *)to, NULL); + if (to == NULL) { Py_DECREF(result); return NULL; } - PyTuple_SET_ITEM(result, i, copyable); + PyTuple_SET_ITEM(result, i, to); } - Py_DECREF(copyfunc); return result; }