On 11/28/2016 05:38 PM, 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.
- 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?).
--Guido
Solution (2) is a very good alternative and can be implemented using a
metapath hook as Steve proposed elsewhere in this thread [0].
We considered a similar metapath hook when designing the PEP, but
decided against it, to better match the current behavior of third-party
modules not being able to replace parts of stdlib.
Note that as Brett says elsewhere in the thread, due to caching there
would be no extra stat() calls in the usual case. On the other hand, we
aren't familiar with Windows, where replacing missing stdlib modules
seems to be standard practice. Thanks for letting us know.
With a metapath hook, .missing.py files are probably overkill, and the
hook can just look at one file (or a static compiled-in list) of
ModuleNotFound/ImportError messages for all missing modules, as M.-A.
Lemburg and others are suggesting. We'll just need to think about
coordinating how the list is generated/updated: the current PEP
implicitly allows other parties, besides Python and the distributors, to
step in cleanly if they need to—needing to update a single list could
lead to messy hacks.
We'll update the PEP to go with solution (2).
[0] https://mail.python.org/pipermail/python-ideas/2016-November/043837.html
Tomas Orsava
On Mon, Nov 28, 2016 at 8:13 AM, Paul Moore <p.f.mo...@gmail.com
<mailto:p.f.mo...@gmail.com>> wrote:
On 28 November 2016 at 15:51, Tomas Orsava <tors...@redhat.com
<mailto:tors...@redhat.com>> wrote:
> I believe I may have found the Windows curses implementation,
it's called
> PDCurses [0], and this website [1] appears to be distributing it
under the
> name `curses`.
My apologies, I should have included a pointer. That is indeed the
distribution I was thinking of.
> Could some Windows user please check if compiling Python with
the current
> reference implementation [2] of this PEP indeed generates a
> `curses.missing.py <http://curses.missing.py>` file among the
stdlib files? If so, we might consider
> skipping the generation of the .missing.py file for the curses
module on
> Windows.
I'll see if I can make some time to do the test. But as the change is
to setup.py, and the Windows build uses Visual Studio project files to
do the build, I expect that it won't generate missing.py files on
Windows. In actual fact, that may be the simplest solution, to note
that the build part of this change is restricted to Unix (non-Windows)
platforms specifically. As there's no real concept of a "distribution
version" of Python on Windows, it's probably not something that will
be that important on that platform (and support for .missing.py files
is there, it would just be necessary for distributors to manually
create those files as needed).
Paul
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