Add Nick's feedback.

pep-0559.rst

@@ -60,6 +60,24 @@ you return ``7`` or ``((7,), {})``?  And so on.
 The author claims that you won't ever need the return value of ``noop()`` so
 it will always return ``None``.
 
+Coghlin's Dialogs (edited for formatting):
+
+    My counterargument to this would be ``map(noop, iterable)``,
+    ``sorted(iterable, key=noop)``, etc. (``filter``, ``max``, and
+    ``min`` all accept callables that accept a single argument, as do
+    many of the itertools operations).
+
+    Making ``noop()`` a useful default function in those cases just
+    needs the definition to be::
+
+       def noop(*args, **kwds):
+           return args[0] if args else None
+
+    The counterargument to the counterargument is that using ``None``
+    as the default in all these cases is going to be faster, since it
+    lets the algorithm skip the callback entirely, rather than calling
+    it and having it do nothing useful.
+
 
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