PEP: 336 Title: Make None Callable Version: $Revision$ Last-Modified: $Date$ Author: Andrew McClelland Status: Rejected 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. BDFL Pronouncement This PEP is rejected. It is considered a feature that None raises an error when called. The proposal falls short in tests for obviousness, clarity, explictness, and necessity. The provided Switch example is nice but easily handled by a simple lambda definition. See python-dev discussion on 17 June 2005. 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/reference/ Copyright This document has been placed in the public domain. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 End: