On 12/05/2016 01:42 PM, Nick Coghlan wrote:
On 5 December 2016 at 19:56, Tomas Orsava <tors...@redhat.com> wrote:
On 12/03/2016 05:08 AM, Nick Coghlan wrote:
Though I believe the default sys.excepthook function is currently written
in
C, so it wouldn't be very easy for distributors to customize it. Maybe it
could be made to read module=error_message pairs from some external file,
which would be easier to modify?
The default implementation is written in C, but distributors could
patch site.py to replace it with a custom one written in Python. For
example, publish a "fedora-hooks" module to PyPI (so non-system Python
installations or applications regularly run without the site module
can readily use the same hooks if they choose to do so), and then
patch site.py in the system Python to do:
import fedora_hooks
fedora_hooks.install_excepthook()
The nice thing about that approach is it wouldn't need a new switch to
turn it off - it would get turned off with all the other site-specific
customisations when -S or -I is used. It would also better open things
up to redistributor experimentation in existing releases (2.7, 3.5,
etc) before we commit to a specific approach in the reference
interpreter (such as adding an optional 'platform.hooks' submodule
that vendors may provide, and relevant stdlib APIs will then call
automatically to override the default upstream provided processing).
Ah, but of course! That leaves us with only one part of the PEP unresolved:
When the build process is unable to compile some modules when building
Python from source (such as _sqlite3 due to missing sqlite headers), it
would be great to provide a custom message when one then tries to import
such module when using the compiled Python.
Do you see a 'pretty' solution for that within this framework?
I'm not sure it qualifies as 'pretty', but one approach would be to
have a './Modules/missing/' directory that gets pre-populated with
checked in "<name>.py" files for extension modules that aren't always
built. When getpath.c detects it's running from a development
checkout, it would add that directory to sys.path (just before
site-packages), while 'make install' and 'make altinstall' would only
copy files from that directory into the installation target if the
corresponding extension modules were missing.
Essentially, that would be the "name.missing.py" part of the draft
proposal for optional standard library modules, just with a regular
"name.py" module name and a tweak to getpath.c.
To my eye that looks like a complicated mechanism necessitating changes
to several parts of the codebase. Have you considered modifying the
default sys.excepthook implementation to read a list of modules and
error messages from a file that was generated during the build process?
To me that seems simpler, and the implementation will be only in one place.
In addition, distributors could just populate that file with their data,
thus we would have one mechanism for both use cases.
Tomas
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