bpo-36144: Dictionary Union (PEP 584)

Lib/collections/__init__.py

@@ -979,6 +979,26 @@ def __contains__(self, key):
 
     # Now, add the methods in dicts but not in MutableMapping
     def __repr__(self): return repr(self.data)
+
+    def __or__(self, other):
+        if isinstance(other, UserDict):
+            return self.__class__(self.data | other.data)
+        if isinstance(other, type(self.data)):
+            return self.__class__(self.data | other)
+        return NotImplemented
+    def __ror__(self, other):
+        if isinstance(other, UserDict):
+            return self.__class__(other.data | self.data)
+        if isinstance(other, type(self.data)):
+            return self.__class__(other | self.data)
+        return NotImplemented
+    def __ior__(self, other):
+        if isinstance(other, UserDict):
+            self.data |= other.data
+        else:
+            self.data |= other
+        return self
+
     def __copy__(self):
         inst = self.__class__.__new__(self.__class__)
         inst.__dict__.update(self.__dict__)

Lib/test/test_dict.py

@@ -37,6 +37,36 @@ def test_literal_constructor(self):
             dictliteral = '{' + ', '.join(formatted_items) + '}'
             self.assertEqual(eval(dictliteral), dict(items))
 
+    def test_merge_operator(self):
+
+        a = {0: 0, 1: 1, 2: 1}
+        b = {1: 1, 2: 2, 3: 3}
+
+        c = a.copy()
+        c |= b
+
+        self.assertEqual(a | b, {0: 0, 1: 1, 2: 2, 3: 3})
+        self.assertEqual(c, {0: 0, 1: 1, 2: 2, 3: 3})
+
+        c = b.copy()
+        c |= a
+
+        self.assertEqual(b | a, {1: 1, 2: 1, 3: 3, 0: 0})
+        self.assertEqual(c, {1: 1, 2: 1, 3: 3, 0: 0})
+
+        c = a.copy()
+        c |= [(1, 1), (2, 2), (3, 3)]
+
+        self.assertEqual(c, {0: 0, 1: 1, 2: 2, 3: 3})
+
+        self.assertIs(a.__or__(None), NotImplemented)
+        self.assertIs(a.__or__(()), NotImplemented)
+        self.assertIs(a.__or__("BAD"), NotImplemented)
+
+        self.assertRaises(TypeError, a.__ior__, None)
+        self.assertEqual(a.__ior__(()), {0: 0, 1: 1, 2: 1})
+        self.assertRaises(ValueError, a.__ior__, "BAD")
+
     def test_bool(self):
         self.assertIs(not {}, True)
         self.assertTrue({1: 2})

Misc/NEWS.d/next/Core and Builtins/2019-03-02-23-03-34.bpo-36144.LRl4LS.rst

@@ -0,0 +1,2 @@
+:class:`dict` (and :class:`collections.UserDict`) objects now support PEP 584's merge (``|``) and update (``|=``) operators.
+Patch by Brandt Bucher.

Objects/dictobject.c

@@ -2310,6 +2310,25 @@ dict_fromkeys_impl(PyTypeObject *type, PyObject *iterable, PyObject *value)
     return _PyDict_FromKeys((PyObject *)type, iterable, value);
 }
 
+/* Single-arg dict update; used by dict_update_common and operators. */
+static int
+dict_update_arg(PyObject *self, PyObject *arg)
+{
+    if (PyDict_CheckExact(arg)) {
+        return PyDict_Merge(self, arg, 1);
+    }
+    _Py_IDENTIFIER(keys);
+    PyObject *func;
+    if (_PyObject_LookupAttrId(arg, &PyId_keys, &func) < 0) {
+        return -1;
+    }
+    if (func != NULL) {
+        Py_DECREF(func);
+        return PyDict_Merge(self, arg, 1);
+    }
+    return PyDict_MergeFromSeq2(self, arg, 1);
+}
+
 static int
 dict_update_common(PyObject *self, PyObject *args, PyObject *kwds,
                    const char *methname)
@@ -2321,23 +2340,7 @@ dict_update_common(PyObject *self, PyObject *args, PyObject *kwds,
         result = -1;
     }
     else if (arg != NULL) {
-        if (PyDict_CheckExact(arg)) {
-            result = PyDict_Merge(self, arg, 1);
-        }
-        else {
-            _Py_IDENTIFIER(keys);
-            PyObject *func;
-            if (_PyObject_LookupAttrId(arg, &PyId_keys, &func) < 0) {
-                result = -1;
-            }
-            else if (func != NULL) {
-                Py_DECREF(func);
-                result = PyDict_Merge(self, arg, 1);
-            }
-            else {
-                result = PyDict_MergeFromSeq2(self, arg, 1);
-            }
-        }
+        result = dict_update_arg(self, arg);
     }
 
     if (result == 0 && kwds != NULL) {
@@ -3157,6 +3160,33 @@ dict_sizeof(PyDictObject *mp, PyObject *Py_UNUSED(ignored))
     return PyLong_FromSsize_t(_PyDict_SizeOf(mp));
 }
 
+static PyObject *
+dict_or(PyObject *self, PyObject *other)
+{
+    if (!PyDict_Check(self) || !PyDict_Check(other)) {
+        Py_RETURN_NOTIMPLEMENTED;
+    }
+    PyObject *new = PyDict_Copy(self);
+    if (new == NULL) {
+        return NULL;
+    }
+    if (dict_update_arg(new, other)) {
+        Py_DECREF(new);
+        return NULL;
+    }
+    return new;
+}
+
+static PyObject *
+dict_ior(PyObject *self, PyObject *other)
+{
+    if (dict_update_arg(self, other)) {
+        return NULL;
+    }
+    Py_INCREF(self);
+    return self;
+}
+
 PyDoc_STRVAR(getitem__doc__, "x.__getitem__(y) <==> x[y]");
 
 PyDoc_STRVAR(sizeof__doc__,
@@ -3262,6 +3292,11 @@ static PySequenceMethods dict_as_sequence = {
     0,                          /* sq_inplace_repeat */
 };
 
+static PyNumberMethods dict_as_number = {
+    .nb_or = dict_or,
+    .nb_inplace_or = dict_ior,
+};
+
 static PyObject *
 dict_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 {
@@ -3323,7 +3358,7 @@ PyTypeObject PyDict_Type = {
     0,                                          /* tp_setattr */
     0,                                          /* tp_as_async */
     (reprfunc)dict_repr,                        /* tp_repr */
-    0,                                          /* tp_as_number */
+    &dict_as_number,                            /* tp_as_number */
     &dict_as_sequence,                          /* tp_as_sequence */
     &dict_as_mapping,                           /* tp_as_mapping */
     PyObject_HashNotImplemented,                /* tp_hash */