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bpo-40273: Reversible mappingproxy #19513

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May 8, 2020
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bpo-40273: Reversible mappingproxy #19513

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bpo-40273: Reversible mappingproxy
ZackerySpytz Apr 14, 2020
4bb8a2e
Merge remote-tracking branch 'upstream/master' into bpo-40273-mapping…
ZackerySpytz May 6, 2020
5fdafb5
Address comments.
ZackerySpytz May 6, 2020
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8 changes: 8 additions & 0 deletions Lib/test/test_types.py
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Original file line number Diff line number Diff line change
Expand Up @@ -627,6 +627,7 @@ def test_methods(self):
'__iter__',
'__len__',
'__or__',
'__reversed__',
'__ror__',
'copy',
'get',
Expand Down Expand Up @@ -768,6 +769,13 @@ def test_iterators(self):
self.assertEqual(set(view.values()), set(values))
self.assertEqual(set(view.items()), set(items))

def test_reversed(self):
d = {'a': 1, 'b': 2, 'foo': 0, 'c': 3, 'd': 4}
del d['foo']
r = reversed(self.mappingproxy(d))
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I think creating the proxy before deleting the element makes sure that this is indeed an updating view:

Suggested change
del d['foo']
r = reversed(self.mappingproxy(d))
mp = self.mappingproxy(d)
del d['foo']
r = reversed(mp)

self.assertEqual(list(r), list('dcba'))
self.assertRaises(StopIteration, next, r)

def test_copy(self):
original = {'key1': 27, 'key2': 51, 'key3': 93}
view = self.mappingproxy(original)
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2020-04-14-09-54-35.bpo-40273.IN73Ks.rst
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@@ -0,0 +1 @@
:class:`types.MappingProxyType` is now reversible.
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This needs a versionchanged entry in the main docs as well.

9 changes: 9 additions & 0 deletions Objects/descrobject.c
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Expand Up @@ -1077,6 +1077,13 @@ mappingproxy_copy(mappingproxyobject *pp, PyObject *Py_UNUSED(ignored))
return _PyObject_CallMethodIdNoArgs(pp->mapping, &PyId_copy);
}

static PyObject *
mappingproxy_reversed(mappingproxyobject *pp, PyObject *Py_UNUSED(ignored))
{
_Py_IDENTIFIER(__reversed__);
return _PyObject_CallMethodIdNoArgs(pp->mapping, &PyId___reversed__);
}

/* WARNING: mappingproxy methods must not give access
to the underlying mapping */

Expand All @@ -1094,6 +1101,8 @@ static PyMethodDef mappingproxy_methods[] = {
PyDoc_STR("D.copy() -> a shallow copy of D")},
{"__class_getitem__", (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS,
PyDoc_STR("See PEP 585")},
{"__reversed__", (PyCFunction)mappingproxy_reversed, METH_NOARGS,
PyDoc_STR("D.__reversed__() -> reverse iterator")},
{0}
};

Expand Down