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

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>

> 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:
> > ['get_blocking',
> 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.



Christopher Barker, Ph.D.

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Chris.Barker at noaa.gov
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