[Python-Dev] PEP 362 Third Revision (original) (raw)

Larry Hastings larry at hastings.org
Fri Jun 15 21:31:03 CEST 2012

On 06/15/2012 12:06 PM, Benjamin Peterson wrote:

2012/6/15 Larry Hastings<larry at hastings.org>:

On 06/15/2012 11:46 AM, R. David Murray wrote:

Adding a os.haveopenat seems more reasonable than adding isimplemented to every signature object. And more useful, as well; it provides a much more specific piece of information.

We already have "os.haveopenat"; it's spelled sysconfig.getconfigvar('HAVEOPENAT'). But, assuming I land issue 14626, this leads us to: Q: Can I use the dirfd parameter to os.open? A: Only if sysconfig.getconfigvar('HAVEOPENAT') is true. Q: Can I use the fd parameter to os.utime? A: Only if sysconfig.getconfigvar('HAVEFUTIMENS') or sysconfig.getconfigvar('HAVEFUTIMES') is true. I feel this interface lacks civility. There's no reason this couldn't be wrapped into some sort of os level attribute or function.

No, but how would you spell it in a graceful way? It really is specific to a particular parameter on a particular function. And there are a bunch of parameters that are available if any one of a couple C functions is locally available--fd and follow_symlinks on utime, follow_symlinks on chown. follow_symlinks for stat is available if you have lstat or you're on Windows. ('HAS_LSTAT' isn't set on Windows, we don't use configure there.) So certainly I don't like the idea of just checking if the C function(s) is (are) available.

Note that I'm genuinely interested in your answer--"is_implemented" appears to have a groundswell of anti-support and I rather suspect will be axed. Meantime I still need to solve this problem.

I can't say I like any of these:

os.can_use(os.stat, "fd")  # too generic
os.can_use_fd(os.stat)  # too specific

Binding it to the function itself seems to be Just Right to me. But since they're PyCFunctionObjects I can't add arbitrary attributes.

(Perhaps the right thing would be to take this discussion to issue 14626.)

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