For collections.deque() objects, expose the maxlen parameter as a read-only attribute.
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index ce47bd0..ef1bca2 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -361,6 +361,15 @@
``d.appendleft(d.pop())``.
+ Deque objects also provide one read-only attribute:
+
+ .. attribute:: maxlen
+
+ Maximum size of a deque or *None* if unbounded.
+
+ .. versionadded:: 2.7
+
+
In addition to the above, deques support iteration, pickling, ``len(d)``,
``reversed(d)``, ``copy.copy(d)``, ``copy.deepcopy(d)``, membership testing with
the :keyword:`in` operator, and subscript references such as ``d[-1]``. Indexed
diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index a9e010e..fab5a7c 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -105,6 +105,16 @@
d.extendleft(it)
self.assertEqual(list(it), [])
+ def test_maxlen_attribute(self):
+ self.assertEqual(deque().maxlen, None)
+ self.assertEqual(deque('abc').maxlen, None)
+ self.assertEqual(deque('abc', maxlen=4).maxlen, 4)
+ self.assertEqual(deque('abc', maxlen=2).maxlen, 2)
+ self.assertEqual(deque('abc', maxlen=0).maxlen, 0)
+ with self.assertRaises(AttributeError):
+ d = deque('abc')
+ d.maxlen = 10
+
def test_comparisons(self):
d = deque('xabc'); d.popleft()
for e in [d, deque('abc'), deque('ab'), deque(), list(d)]:
diff --git a/Misc/NEWS b/Misc/NEWS
index ad28735..b870bcf 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -195,6 +195,8 @@
Library
-------
+- collections.deque() objects now have a read-only attribute called maxlen.
+
- Issue #2638: Show a window constructed with tkSimpleDialog.Dialog only after
it is has been populated and properly configured in order to prevent
window flashing.
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index 8d27b88..f8d656c 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -812,6 +812,20 @@
return 0;
}
+static PyObject *
+deque_get_maxlen(dequeobject *deque)
+{
+ if (deque->maxlen == -1)
+ Py_RETURN_NONE;
+ return PyLong_FromSsize_t(deque->maxlen);
+}
+
+static PyGetSetDef deque_getset[] = {
+ {"maxlen", (getter)deque_get_maxlen, (setter)NULL,
+ "maximum size of a deque or None if unbounded"},
+ {0}
+};
+
static PySequenceMethods deque_as_sequence = {
(lenfunc)deque_len, /* sq_length */
0, /* sq_concat */
@@ -893,7 +907,7 @@
0, /* tp_iternext */
deque_methods, /* tp_methods */
0, /* tp_members */
- 0, /* tp_getset */
+ deque_getset, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */