Abstract

None should be a callable object that when called with anyarguments has no side effect and returnsNone.

BDFL Pronouncement

This PEP is rejected. It is considered a feature thatNone raisesan error when called. The proposal falls short in tests forobviousness, clarity, explicitness, and necessity. The provided Switchexample is nice but easily handled by a simple lambda definition.See python-dev discussion on 17 June 2005[1].

Motivation

To allow a programming style for selectable actions that is morein accordance with the minimalistic functional programming goalsof the Python language.

Rationale

Allow the use ofNone in method tables as a universal no effectrather than either (1) checking a method table entry againstNonebefore calling, or (2) writing a local no effect method witharguments similar to other functions in the table.

The semantics would be effectively:

classNone:def__call__(self,*args):pass

How To Use

Before, checking function table entry againstNone:

classSelect:defa(self,input):print'a'defb(self,input):print'b'defc(self,input):print'c'def__call__(self,input):function={1:self.a,2:self.b,3:self.c}.get(input,None)iffunction:returnfunction(input)

Before, using a local no effect method:

classSelect:defa(self,input):print'a'defb(self,input):print'b'defc(self,input):print'c'defnop(self,input):passdef__call__(self,input):return{1:self.a,2:self.b,3:self.c}.get(input,self.nop)(input)

After:

classSelect:defa(self,input):print'a'defb(self,input):print'b'defc(self,input):print'c'def__call__(self,input):return{1:self.a,2:self.b,3:self.c}.get(input,None)(input)

References

Copyright

This document has been placed in the public domain.