PEP 572: Weaken proposal / strengthen requirements from "target" to "name"

pep-0572.rst

@@ -35,9 +35,8 @@ Syntax and semantics
 ====================
 
 In any context where arbitrary Python expressions can be used, a **named
-expression** can appear. This is of the form ``target := expr`` where
+expression** can appear. This is of the form ``name := expr`` where
-``expr`` is any valid Python expression, and ``target`` is any valid
+``expr`` is any valid Python expression, and ``name`` is an identifier.
-assignment target.
 
 The value of such a named expression is the same as the incorporated
 expression, with the additional side-effect that the target is assigned
@@ -70,6 +69,15 @@ and is therefore processed right-to-left, as if it were spelled thus::
 
     assert 0 == (x := (y := (z := 0)))
 
+Statement assignment can include annotations. This would be syntactically
+noisy in expressions, and is of minor importance. An annotation can be
+given separately from the assignment if needed::
+
+    x:str = "" # works
+    (x:str := "") # SyntaxError
+    x:str # possibly before a loop
+    (x := "") # fine
+
 Augmented assignment is not supported in expression form::
 
     >>> x +:= 1
@@ -78,6 +86,10 @@ Augmented assignment is not supported in expression form::
             ^
     SyntaxError: invalid syntax
 
+Statement assignment is able to set attributes and subscripts, but
+expression assignment is restricted to names. (This restriction may be
+relaxed in a future version of Python.)
+
 Otherwise, the semantics of assignment are identical in statement and
 expression forms.
 
@@ -522,8 +534,7 @@ With assignment expressions, why bother with assignment statements?
 
 The two forms have different flexibilities.  The ``:=`` operator can be used
 inside a larger expression; the ``=`` statement can be augmented to ``+=`` and
-its friends. The assignment statement is a clear declaration of intent: this
+its friends, can be chained, and can assign to attributes and subscripts.
-value is to be assigned to this target, and that's it.
 
 
 Why not use a sublocal scope and prevent namespace pollution?
@@ -550,9 +561,9 @@ suggestions to move the proposal in this direction. [2]_)
 Style guide recommendations
 ===========================
 
-As this adds another way to spell some of the same effects as can already be
+As expression assignments can be used somewhat equivalently to statement
-done, it is worth noting a few broad recommendations. These could be included
+assignments, the question of which should be preferred will arise. For the
-in PEP 8 and/or other style guides.
+benefit of style guides such as PEP 8, two recommendations are suggested.
 
 1. If either assignment statements or assignment expressions can be
    used, prefer statements; they are a clear declaration of intent.