https://github.com/python/cpython/commit/7bc99dd49ed4cebe4795cc7914c4231209b2aa4b
commit: 7bc99dd49ed4cebe4795cc7914c4231209b2aa4b
branch: 3.13
author: Raymond Hettinger <[email protected]>
committer: rhettinger <[email protected]>
date: 2024-10-08T14:11:43-05:00
summary:
[3.13] Tee of tee was not producing n independent iterators (gh-123884)
(gh-125081)
files:
A Misc/NEWS.d/next/Library/2024-09-24-22-38-51.gh-issue-123884.iEPTK4.rst
M Doc/library/itertools.rst
M Lib/test/test_itertools.py
M Modules/itertoolsmodule.c
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index ceaab2f3e72454..8eb8d07b3fb064 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))
-
- 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
-
- 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.
+ raise ValueError
+ if n == 0:
+ return ()
+ iterator = _tee(iterable)
+ result = [iterator]
+ for _ in range(n - 1):
+ result.append(_tee(iterator))
+ return tuple(result)
+
+ 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
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/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 2c8752d215dc69..1e58354b43c14f 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -1642,10 +1642,11 @@ def test_tee(self):
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')
@@ -2072,21 +2073,36 @@ def test_tee_recipe(self):
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)
+
+ 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 _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
+ 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 #############################################
@@ -2132,12 +2148,10 @@ def _tee(iterator, link):
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)
@@ -2158,21 +2172,19 @@ def _tee(iterator, link):
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 00000000000000..55f1d4b41125c3
--- /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 0d6ff20489aa2c..2d4587c1a91bc0 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -1173,7 +1173,7 @@ 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");
@@ -1190,41 +1190,24 @@ 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);
+ (void)&_Py_ID(__copy__); // Retain a reference to __copy__
+ 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;
}
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