[Python-ideas] PEP: Distributing a Subset of the Standard Library

[Terry Reedy]

On 11/28/2016 11:38 AM, Guido van Rossum wrote:
> Overall I think this is a good idea. I have one hit:
>
> It seems that there are two possible strategies for searching the
> .missing.py file:
>
> 1. (Currently in the PEP) search it at the same time as the .py file
> when walking along sys.path.
>   - Pro: prevents confusion when the user accidentally has their own
> matching file later in sys.path.
>   - Con: prevents the user from installing a matching file intentionally
> (e.g. a 3rd party version).
>
> 2. After exhausting sys.path, search it again just for .missing.py files
> (or perhaps remember the location of the .missing.py file during the
> first search but don't act immediately on it -- this has the same effect).
>   - Pro: allows user to install their own version.

The Windows distribution. for instance, could have a mod.missing.py file 
for every non-Windows, unix-only module.  This would cut down on 'Why 
did this import fail?' questions on SO and python-list.  And without 
breaking anything. Even for non-beginners, it would save having to look 
up whether the an import failure is inherent on the platform or due to a 
typo.

>   - Con: if the user has a matching file by accident, that file will be
> imported, causing more confusion.
>
> I personally would weigh these so as to prefer (2). The option of
> installing your own version when the standard version doesn't exist
> seems reasonable; there may be reasons that you can't or don't want to
> install the distribution's version. I don't worry much about the danger
> of accidental name conflicts (have you ever seen this?).

The accidental conflict reports I have seen were due to scripts in as 
in the same directory as the program, rather than modules in site-packages.
-- 
Terry Jan Reedy