[Python-Dev] Updated PEP 362 (Function Signature Object) (original) (raw)

Larry Hastings larry at hastings.org
Wed Jun 6 18:36:15 CEST 2012

On 06/06/2012 09:05 AM, Larry Hastings wrote:

Is there a use-case for isimplemented? Yes, see issue 14626.

I should add, there are already some places in the standard library where is_implemented would be relevant. The "mode" argument to os.mkdir comes immediately to mind; on Windows it is accepted but ignored. A counter-example would be os.symlink, which takes an extra parameter on Windows that's not even accepted on other platforms.

I am utterly convinced that, when faced with these sorts of platform-specific API differences, the first step towards sanity is to have the API accept a consistent signature everywhere. What you do after that is up for debate--in most cases where the parameter causes a significant semantic change, I think specifying it with a non-default value should throw a NotImplementedError. (With the specific case of os.mkdir on Windows, I can agree with silently ignoring the mode; it's not like the hapless Windows programmer could react and take a useful alternative approach.)

Parameter objects exposing is_implemented allows LBYL in these situations, rather than having to react to NotImplementedError.

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