[Python-Dev] PEP 549: Instance Properties (aka: module properties) (original) (raw)

Chris Barker chris.barker at noaa.gov
Mon Sep 11 16:32:36 EDT 2017

On Mon, Sep 11, 2017 at 10:20 AM, Victor Stinner <victor.stinner at gmail.com> wrote:

2017-09-11 19:00 GMT+02:00 Chris Barker <chris.barker at noaa.gov>: > There are a heck of a lot in the os module: > ['getblocking',

This one is not a good example: it takes a parameter. You cannot convert it to a property.

I'm sure there are many that really do have a good reason for a getter function, but not all, by any means.

When designing an API, when I have to choose between property and

function/method, I prefer function/method over a property when the code is slow, especially at the first call.

I prefer to "warn" users than a call (like the first one which fills a cache) can be slow. Well, it's not a strong rule, sometimes I use a property even if the first call has to fill a cache :-) Here the sysconfig has to build an internal cache at the first call ... if I recall correctly.

If we do get properties on modules, then there is plenty of room to discuss best API for a given functionality. And chances are, we won't gratuitously re-factor the standard library.

But your point is well taken, and makes my point in a way -- if we had properties, then there would be a getter function only if there was a good reason for it. As it stands, I have no idea if calling, for instance, sysconfig.get_config_vars is an expensive operation.

-CHB

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Christopher Barker, Ph.D. Oceanographer

Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception

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