[Python-checkins] python/nondist/peps pep-0336.txt, NONE, 1.1 pep-0000.txt, 1.293, 1.294

[goodger at users.sourceforge.net]

Update of /cvsroot/python/python/nondist/peps
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv20583

Modified Files:
	pep-0000.txt 
Added Files:
	pep-0336.txt 
Log Message:
added PEP 336, "Make None Callable", by Andrew McClelland

--- NEW FILE: pep-0336.txt ---
PEP: 336
Title: Make None Callable
Version: $Revision: 1.1 $
Last-Modified: $Date: 2004/11/03 16:58:30 $ 
Author: Andrew McClelland
Status: Draft
Type: Standards Track
Content-Type: text/plain 
Created: 28-Oct-2004
Post-History: 


Abstract

    None should be a callable object that when called with any
    arguments has no side effect and returns None.


Motivation

    To allow a programming style for selectable actions that is more
    in accordance with the minimalistic functional programming goals
    of the Python language.


Rationale

    Allow the use of None in method tables as a universal no effect
    rather than either (1) checking a method table entry against None
    before calling, or (2) writing a local no effect method with
    arguments similar to other functions in the table.

    The semantics would be effectively,

        class None:

            def __call__(self, *args):
                pass


How To Use

    Before, checking function table entry against None:

        class Select:

            def a(self, input):
                print 'a'

            def b(self, input):
                print 'b'

            def c(self, input);
                print 'c'

            def __call__(self, input):
                function = { 1 : self.a,
                         2 : self.b,
                         3 : self.c
                       }.get(input, None)
                if function:  return function(input)

    Before, using a local no effect method:

        class Select:

            def a(self, input):
                print 'a'

            def b(self, input):
                print 'b'

            def c(self, input);
                print 'c'

            def nop(self, input):
                pass

            def __call__(self, input):
                return { 1 : self.a,
                     2 : self.b,
                     3 : self.c
                       }.get(input, self.nop)(input)

    After:

        class Select:

            def a(self, input):
                print 'a'

            def b(self, input):
                print 'b'

            def c(self, input);
                print 'c'

            def __call__(self, input):
                return { 1 : self.a,
                     2 : self.b,
                     3 : self.c
                       }.get(input, None)(input)


References

    [1] Python Reference Manual, Section 3.2,
        http://docs.python.org/ref/ref.html


Copyright

    This document has been placed in the public domain.



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Index: pep-0000.txt
===================================================================
RCS file: /cvsroot/python/python/nondist/peps/pep-0000.txt,v
retrieving revision 1.293
retrieving revision 1.294
diff -u -d -r1.293 -r1.294
--- pep-0000.txt	27 Oct 2004 10:09:55 -0000	1.293
+++ pep-0000.txt	3 Nov 2004 16:58:30 -0000	1.294
@@ -123,6 +123,7 @@
  S   332  Byte vectors and String/Unicode Unification  Montanaro
  S   334  Simple Coroutines via SuspendIteration       Evans
  S   335  Overloadable Boolean Operators               Ewing
+ S   336  Make None Callable                           McClelland
  S   754  IEEE 754 Floating Point Special Values       Warnes
 
  Finished PEPs (done, implemented in CVS)
@@ -366,6 +367,7 @@
  I   333  Python Web Server Gateway Interface v1.0     Eby
  S   334  Simple Coroutines via SuspendIteration       Evans
  S   335  Overloadable Boolean Operators               Ewing
+ S   336  Make None Callable                           McClelland
  SR  666  Reject Foolish Indentation                   Creighton
  S   754  IEEE 754 Floating Point Special Values       Warnes
  I  3000  Python 3.0 Plans                             Kuchling, Cannon
@@ -431,6 +433,7 @@
     Lielens, Gregory         gregory.lielens at fft.be
     von Loewis, Martin       loewis at informatik.hu-berlin.de
     Martelli, Alex           aleax at aleax.it
+    McClelland, Andrew       eternalsquire at comcast.net
     McMillan, Gordon         gmcm at hypernet.com
     McNamara, Andrew         andrewm at object-craft.com.au
     Mick, Trent              trentm at activestate.com