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Fri Jun 15 12:51:16 CEST 2012 · https://mail.python.org/pipermail/python-dev/2012-June/120289.html

On 06/15/2012 12:18 AM, Nick Coghlan wrote:
>> Perhaps you meant "ill-concieved"?
> No, I mean ill-defined. The criteria for when a particular platform
> should flip that bit for an arbitrary parameter is highly unclear, as
> whether or not a particular parameter is "implemented" or not depends
> on the operation and the parameter.

I guess I really did do a poor job of explaining it then.  Here's 
another pass.

My working definition for "is_implemented" is "is this functionality 
available at all?"  Pressed to produce a stricter definition, I *would* 
define "is_implemented" as:

    True if it is possible to produce any valid inputs for the parameter
    on the current platform, and False otherwise.

However, I don't think parameters should be added and removed from a 
function's signature based on what functionality is available on the 
local platform--that way lies madness.  Instead I think it best to 
define a no-op default value for every optional parameter, and always 
accept that even when the functionality behind it isn't locally 
available.    Function signatures should be stable.  Therefore I amend 
the definition to:

    True if it is possible to produce any valid non-default inputs for
    the parameter on the current platform, and False otherwise.

If I understand you correctly, you seem to be trying to apply 
"is_implemented" to the problem of predicting which specific inputs to a 
parameter would be valid.  I don't think that problem is tractable--it's 
way too context-specific.

//arry/
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[Python-Dev] PEP 362 Third Revision