PEP 572: Update implementation notes and add an example

pep-0572.rst

@@ -117,7 +117,7 @@ These list comprehensions are all approximately equivalent::
     def g():
         for x in range(5):
             y = f(x)
-            yield [y, y]
+            yield [y, x/y]
     stuff = list(g)
 
     # Using a statement-local name
@@ -135,6 +135,18 @@ avoided when ``def`` is an option.  As the name's scope extends to the full
 current statement, even a block statement, this can be used to good effect
 in the header of an ``if`` or ``while`` statement::
 
+    # Current Python, not caring about function return value
+    while input("> ") != "quit":
+        print("You entered a command.")
+
+    # Current Python, capturing return value - four-line loop header
+    while True:
+        command = input("> ");
+	if command == "quit":
+	    break
+        print("You entered:", command)
+
+    # Proposed alternative to the above
     while (input("> ") as command) != "quit":
         print("You entered:", command)
 
@@ -263,11 +275,9 @@ Discrepancies in the current implementation
 ===========================================
 
 1. SLNBs are implemented using a special (and mostly-invisible) name
-   mangling.  This works perfectly inside functions (including list
-   comprehensions), but not at top level.  Making this work at top-level
-   and in class definitions would be very much of value.
-
-2. Assigning 'through' a SLNB is not implemented yet.
+   mangling.  They may sometimes appear in globals() and/or locals() with
+   their simple or mangled names (but buggily and unreliably). They should
+   be suppressed as though they were guinea pigs.
 
 
 References