[Python-checkins] bpo-38200: Add itertools.pairwise() (GH-23549)
rhettinger
webhook-mailer at python.org
Mon Nov 30 23:43:00 EST 2020
https://github.com/python/cpython/commit/cc061d0e6fb2569efa91531686f75b89e94ec865
commit: cc061d0e6fb2569efa91531686f75b89e94ec865
branch: master
author: Raymond Hettinger <rhettinger at users.noreply.github.com>
committer: rhettinger <rhettinger at users.noreply.github.com>
date: 2020-11-30T20:42:54-08:00
summary:
bpo-38200: Add itertools.pairwise() (GH-23549)
files:
A Misc/NEWS.d/next/Library/2020-11-28-22-52-57.bpo-38200.DuWGlW.rst
M Doc/library/itertools.rst
M Lib/test/test_itertools.py
M Modules/clinic/itertoolsmodule.c.h
M Modules/itertoolsmodule.c
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index 3de66c9349281..44728b42287bc 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -55,6 +55,7 @@ Iterator Arguments Results
:func:`filterfalse` pred, seq elements of seq where pred(elem) is false ``filterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8``
:func:`groupby` iterable[, key] sub-iterators grouped by value of key(v)
:func:`islice` seq, [start,] stop [, step] elements from seq[start:stop:step] ``islice('ABCDEFG', 2, None) --> C D E F G``
+:func:`pairwise` iterable (p[0], p[1]), (p[1], p[2]) ``pairwise('ABCDEFG') --> AB BC CD DE EF FG``
:func:`starmap` func, seq func(\*seq[0]), func(\*seq[1]), ... ``starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000``
:func:`takewhile` pred, seq seq[0], seq[1], until pred fails ``takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4``
:func:`tee` it, n it1, it2, ... itn splits one iterator into n
@@ -475,6 +476,22 @@ loops that truncate the stream.
If *start* is ``None``, then iteration starts at zero. If *step* is ``None``,
then the step defaults to one.
+.. function:: pairwise(iterable)
+
+ Return successive overlapping pairs taken from the input *iterable*.
+
+ The number of 2-tuples in the output iterator will be one fewer than the
+ number of inputs. It will be empty if the input iterable has fewer than
+ two values.
+
+ Roughly equivalent to::
+
+ def pairwise(iterable):
+ # pairwise('ABCDEFG') --> AB BC CD DE EF FG
+ a, b = tee(iterable)
+ next(b, None)
+ return zip(a, b)
+
.. function:: permutations(iterable, r=None)
@@ -782,12 +799,6 @@ which incur interpreter overhead.
return starmap(func, repeat(args))
return starmap(func, repeat(args, times))
- def pairwise(iterable):
- "s -> (s0,s1), (s1,s2), (s2, s3), ..."
- a, b = tee(iterable)
- next(b, None)
- return zip(a, b)
-
def grouper(iterable, n, fillvalue=None):
"Collect data into fixed-length chunks or blocks"
# grouper('ABCDEFG', 3, 'x') --> ABC DEF Gxx"
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 702cf0820316b..df2997e87d494 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -1024,6 +1024,25 @@ def run(r1, r2):
self.assertEqual(next(it), (1, 2))
self.assertRaises(RuntimeError, next, it)
+ def test_pairwise(self):
+ self.assertEqual(list(pairwise('')), [])
+ self.assertEqual(list(pairwise('a')), [])
+ self.assertEqual(list(pairwise('ab')),
+ [('a', 'b')]),
+ self.assertEqual(list(pairwise('abcde')),
+ [('a', 'b'), ('b', 'c'), ('c', 'd'), ('d', 'e')])
+ self.assertEqual(list(pairwise(range(10_000))),
+ list(zip(range(10_000), range(1, 10_000))))
+
+ with self.assertRaises(TypeError):
+ pairwise() # too few arguments
+ with self.assertRaises(TypeError):
+ pairwise('abc', 10) # too many arguments
+ with self.assertRaises(TypeError):
+ pairwise(iterable='abc') # keyword arguments
+ with self.assertRaises(TypeError):
+ pairwise(None) # non-iterable argument
+
def test_product(self):
for args, result in [
([], [()]), # zero iterables
@@ -1787,6 +1806,10 @@ def test_islice(self):
a = []
self.makecycle(islice([a]*2, None), a)
+ def test_pairwise(self):
+ a = []
+ self.makecycle(pairwise([a]*5), a)
+
def test_permutations(self):
a = []
self.makecycle(permutations([1,2,a,3], 3), a)
@@ -1995,6 +2018,17 @@ def test_islice(self):
self.assertRaises(TypeError, islice, N(s), 10)
self.assertRaises(ZeroDivisionError, list, islice(E(s), 10))
+ def test_pairwise(self):
+ for s in ("123", "", range(1000), ('do', 1.2), range(2000,2200,5)):
+ for g in (G, I, Ig, S, L, R):
+ seq = list(g(s))
+ expected = list(zip(seq, seq[1:]))
+ actual = list(pairwise(g(s)))
+ self.assertEqual(actual, expected)
+ self.assertRaises(TypeError, pairwise, X(s))
+ self.assertRaises(TypeError, pairwise, N(s))
+ self.assertRaises(ZeroDivisionError, list, pairwise(E(s)))
+
def test_starmap(self):
for s in (range(10), range(0), range(100), (7,11), range(20,50,5)):
for g in (G, I, Ig, S, L, R):
@@ -2312,15 +2346,6 @@ def test_permutations_sizeof(self):
... else:
... return starmap(func, repeat(args, times))
->>> def pairwise(iterable):
-... "s -> (s0,s1), (s1,s2), (s2, s3), ..."
-... a, b = tee(iterable)
-... try:
-... next(b)
-... except StopIteration:
-... pass
-... return zip(a, b)
-
>>> def grouper(n, iterable, fillvalue=None):
... "grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx"
... args = [iter(iterable)] * n
@@ -2451,15 +2476,6 @@ def test_permutations_sizeof(self):
>>> take(5, map(int, repeatfunc(random.random)))
[0, 0, 0, 0, 0]
->>> list(pairwise('abcd'))
-[('a', 'b'), ('b', 'c'), ('c', 'd')]
-
->>> list(pairwise([]))
-[]
-
->>> list(pairwise('a'))
-[]
-
>>> list(islice(pad_none('abc'), 0, 6))
['a', 'b', 'c', None, None, None]
diff --git a/Misc/NEWS.d/next/Library/2020-11-28-22-52-57.bpo-38200.DuWGlW.rst b/Misc/NEWS.d/next/Library/2020-11-28-22-52-57.bpo-38200.DuWGlW.rst
new file mode 100644
index 0000000000000..b4bc5551b2532
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-11-28-22-52-57.bpo-38200.DuWGlW.rst
@@ -0,0 +1 @@
+Added itertools.pairwise()
diff --git a/Modules/clinic/itertoolsmodule.c.h b/Modules/clinic/itertoolsmodule.c.h
index c1192bbcb0d79..82729eeb56bce 100644
--- a/Modules/clinic/itertoolsmodule.c.h
+++ b/Modules/clinic/itertoolsmodule.c.h
@@ -2,6 +2,37 @@
preserve
[clinic start generated code]*/
+PyDoc_STRVAR(pairwise_new__doc__,
+"pairwise(iterable, /)\n"
+"--\n"
+"\n"
+"Return an iterator of overlapping pairs taken from the input iterator.\n"
+"\n"
+" s -> (s0,s1), (s1,s2), (s2, s3), ...");
+
+static PyObject *
+pairwise_new_impl(PyTypeObject *type, PyObject *iterable);
+
+static PyObject *
+pairwise_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
+{
+ PyObject *return_value = NULL;
+ PyObject *iterable;
+
+ if ((type == &pairwise_type) &&
+ !_PyArg_NoKeywords("pairwise", kwargs)) {
+ goto exit;
+ }
+ if (!_PyArg_CheckPositional("pairwise", PyTuple_GET_SIZE(args), 1, 1)) {
+ goto exit;
+ }
+ iterable = PyTuple_GET_ITEM(args, 0);
+ return_value = pairwise_new_impl(type, iterable);
+
+exit:
+ return return_value;
+}
+
PyDoc_STRVAR(itertools_groupby__doc__,
"groupby(iterable, key=None)\n"
"--\n"
@@ -627,4 +658,4 @@ itertools_count(PyTypeObject *type, PyObject *args, PyObject *kwargs)
exit:
return return_value;
}
-/*[clinic end generated code: output=d7f58dc477814b45 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=889c4afc3b13574f input=a9049054013a1b77]*/
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index ce8b4347ef220..7144856c352f8 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -1,4 +1,5 @@
+
#define PY_SSIZE_T_CLEAN
#include "Python.h"
#include "pycore_long.h" // _PyLong_GetZero()
@@ -27,8 +28,9 @@ class itertools.accumulate "accumulateobject *" "&accumulate_type"
class itertools.compress "compressobject *" "&compress_type"
class itertools.filterfalse "filterfalseobject *" "&filterfalse_type"
class itertools.count "countobject *" "&count_type"
+class itertools.pairwise "pairwiseobject *" "&pairwise_type"
[clinic start generated code]*/
-/*[clinic end generated code: output=da39a3ee5e6b4b0d input=ea05c93c6d94726a]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=6498ed21fbe1bf94]*/
static PyTypeObject groupby_type;
static PyTypeObject _grouper_type;
@@ -45,9 +47,140 @@ static PyTypeObject accumulate_type;
static PyTypeObject compress_type;
static PyTypeObject filterfalse_type;
static PyTypeObject count_type;
+static PyTypeObject pairwise_type;
#include "clinic/itertoolsmodule.c.h"
+/* pairwise object ***********************************************************/
+
+typedef struct {
+ PyObject_HEAD
+ PyObject *it;
+ PyObject *old;
+} pairwiseobject;
+
+/*[clinic input]
+ at classmethod
+itertools.pairwise.__new__ as pairwise_new
+ iterable: object
+ /
+Return an iterator of overlapping pairs taken from the input iterator.
+
+ s -> (s0,s1), (s1,s2), (s2, s3), ...
+
+[clinic start generated code]*/
+
+static PyObject *
+pairwise_new_impl(PyTypeObject *type, PyObject *iterable)
+/*[clinic end generated code: output=9f0267062d384456 input=6e7c3cddb431a8d6]*/
+{
+ PyObject *it;
+ pairwiseobject *po;
+
+ it = PyObject_GetIter(iterable);
+ if (it == NULL) {
+ return NULL;
+ }
+ po = (pairwiseobject *)type->tp_alloc(type, 0);
+ if (po == NULL) {
+ Py_DECREF(it);
+ return NULL;
+ }
+ po->it = it;
+ po->old = NULL;
+ return (PyObject *)po;
+}
+
+static void
+pairwise_dealloc(pairwiseobject *po)
+{
+ PyObject_GC_UnTrack(po);
+ Py_XDECREF(po->it);
+ Py_XDECREF(po->old);
+ Py_TYPE(po)->tp_free(po);
+}
+
+static int
+pairwise_traverse(pairwiseobject *po, visitproc visit, void *arg)
+{
+ Py_VISIT(po->it);
+ Py_VISIT(po->old);
+ return 0;
+}
+
+static PyObject *
+pairwise_next(pairwiseobject *po)
+{
+ PyObject *it = po->it;
+ PyObject *old = po->old;
+ PyObject *new, *result;
+
+ if (it == NULL) {
+ return NULL;
+ }
+ if (old == NULL) {
+ po->old = old = (*Py_TYPE(it)->tp_iternext)(it);
+ if (old == NULL) {
+ Py_CLEAR(po->it);
+ return NULL;
+ }
+ }
+ new = (*Py_TYPE(it)->tp_iternext)(it);
+ if (new == NULL) {
+ Py_CLEAR(po->it);
+ Py_CLEAR(po->old);
+ return NULL;
+ }
+ /* Future optimization: Reuse the result tuple as we do in enumerate() */
+ result = PyTuple_Pack(2, old, new);
+ Py_SETREF(po->old, new);
+ return result;
+}
+
+static PyTypeObject pairwise_type = {
+ PyVarObject_HEAD_INIT(&PyType_Type, 0)
+ "itertools.pairwise", /* tp_name */
+ sizeof(pairwiseobject), /* tp_basicsize */
+ 0, /* tp_itemsize */
+ /* methods */
+ (destructor)pairwise_dealloc, /* tp_dealloc */
+ 0, /* tp_vectorcall_offset */
+ 0, /* tp_getattr */
+ 0, /* tp_setattr */
+ 0, /* tp_as_async */
+ 0, /* tp_repr */
+ 0, /* tp_as_number */
+ 0, /* tp_as_sequence */
+ 0, /* tp_as_mapping */
+ 0, /* tp_hash */
+ 0, /* tp_call */
+ 0, /* tp_str */
+ PyObject_GenericGetAttr, /* tp_getattro */
+ 0, /* tp_setattro */
+ 0, /* tp_as_buffer */
+ Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
+ Py_TPFLAGS_BASETYPE, /* tp_flags */
+ pairwise_new__doc__, /* tp_doc */
+ (traverseproc)pairwise_traverse, /* tp_traverse */
+ 0, /* tp_clear */
+ 0, /* tp_richcompare */
+ 0, /* tp_weaklistoffset */
+ PyObject_SelfIter, /* tp_iter */
+ (iternextfunc)pairwise_next, /* tp_iternext */
+ 0, /* tp_methods */
+ 0, /* tp_members */
+ 0, /* tp_getset */
+ 0, /* tp_base */
+ 0, /* tp_dict */
+ 0, /* tp_descr_get */
+ 0, /* tp_descr_set */
+ 0, /* tp_dictoffset */
+ 0, /* tp_init */
+ PyType_GenericAlloc, /* tp_alloc */
+ pairwise_new, /* tp_new */
+ PyObject_GC_Del, /* tp_free */
+};
+
/* groupby object ************************************************************/
@@ -4666,6 +4799,7 @@ groupby(iterable[, keyfunc]) --> sub-iterators grouped by value of keyfunc(v)\n\
filterfalse(pred, seq) --> elements of seq where pred(elem) is False\n\
islice(seq, [start,] stop [, step]) --> elements from\n\
seq[start:stop:step]\n\
+pairwise(s) --> (s[0],s[1]), (s[1],s[2]), (s[2], s[3]), ...\n\
starmap(fun, seq) --> fun(*seq[0]), fun(*seq[1]), ...\n\
tee(it, n=2) --> (it1, it2 , ... itn) splits one iterator into n\n\
takewhile(pred, seq) --> seq[0], seq[1], until pred fails\n\
@@ -4695,6 +4829,7 @@ itertoolsmodule_exec(PyObject *m)
&filterfalse_type,
&count_type,
&ziplongest_type,
+ &pairwise_type,
&permutations_type,
&product_type,
&repeat_type,
More information about the Python-checkins
mailing list