PEP 584: Apply feedback from the Python-Dev discussion. (#1309)

pep-0584.rst

@@ -82,6 +82,21 @@ ChainMap will modify the original dict::
       {'eggs': 999}
 
 
+------------------
+``dict(d1, **d2)``
+------------------
+
+This "neat trick" is not well-known, and only works when ``d2`` is
+entirely string-keyed::
+
+    >>> d1 = {"spam": 1}
+    >>> d2 = {3665: 2}
+    >>> dict(d1, **d2)
+    Traceback (most recent call last):
+      ...
+    TypeError: keywords must be strings
+
+
 =========
 Rationale
 =========
@@ -91,8 +106,10 @@ The new operators will have the same relationship to the
 (``+=``) operators have to ``list.extend``. Note that this is
 somewhat different from the relationship that ``|``/``|=`` have with
 ``set.update``; the authors have determined that allowing the in-place
-operator to accept a wider range of types, as ``list`` does, is a more
-useful design.
+operator to accept a wider range of types (as ``list`` does) is a more
+useful design, and that restricting the types of the binary operator's
+operands (again, as ``list`` does) will help avoid silent errors
+caused by complicated implicit type casting on both sides.
 
 Key conflicts will be resolved by keeping the rightmost value.  This
 matches the existing behavior of similar ``dict`` operations, where
@@ -111,18 +128,18 @@ union is not commutative; in general ``d | e != e | d``.
 
 Similarly, the *iteration order* of the key-value pairs in the
 dictionary will follow the same semantics as the examples above, with
-each newly merged pair being appended (or moved) to the end of the
-current sequence.
+each newly added key (and its value) being appended to the current
+sequence.
 
 
 =============
 Specification
 =============
 
-Dict union will return a new dict containing the left operand merged
-with the right operand, which must be a ``dict`` (or an instance of a
-``dict`` subclass). If a key appears in both operands, the last-seen
-value (i.e. that from the right-hand operand) wins::
+Dict union will return a new ``dict`` consisting of the left operand
+merged with the right operand, each of which must be a ``dict`` (or an
+instance of a ``dict`` subclass). If a key appears in both operands,
+the last-seen value (i.e. that from the right-hand operand) wins::
 
     >>> d = {'spam': 1, 'eggs': 2, 'cheese': 3}
     >>> e = {'cheese': 'cheddar', 'aardvark': 'Ethel'}
@@ -166,19 +183,19 @@ An *approximate* pure-Python implementation is::
     def __or__(self, other):
         if not isinstance(other, dict):
             return NotImplemented
-        new = self.copy()
+        new = dict(self)
         new.update(other)
         return new
 
     def __ror__(self, other):
         if not isinstance(other, dict):
             return NotImplemented
-        new = other.copy()
+        new = dict(other)
         new.update(self)
         return new
 
     def __ior__(self, other):
-        self.update(other)
+        dict.update(self, other)
         return self