On 1/07/2011 7:20 PM, Vinay Sajip wrote:
Mark Hammond gmail.com> writes:
The intention is that there only be a single launcher, as only one app
can be associated with .py files. OTOH though, file associations can be
configured per-user IIRC, and assuming that is the case, we could avoid
my multiple-ini-file usecase above by just allowing a different launcher
to be registered for a specific user. This is sounding difficult from
the UI perspective though (ie, does the installer then need to ask that
question, will there be a post-install technique for per-user
registration, etc?)
I don't like this, for the reasons you state. I think it would be better if the
PEP was changed to say that there is intended to be just one launcher
installation per machine. As the intention is for the launcher to ship with
Python, and there can be multiple Pythons installed, I presume we'll have to
handle this by installing the launcher in some common-to-all-Pythons location
somewhere outside a Python installation location, such as "c:\Program
Files\Python Launcher". This should be stated in the PEP, and we'll also need to
indicate how the launcher will be cleaned up if for some strange reason someone
uninstalls all Pythons from a machine. Then we can just state that there's a
global .ini file (where the launcher is installed) and a local one (in the
user's APPDATA). From that perspective, it makes sense to have items in the
local (APPDATA) override the global (launcher installation location).
The PEP does say "if possible, should be installed somewhere likely to
already be on the system PATH (eg., the Windows System32) directory."
It is silent about what to do when that isn't possible, but I'd think it
OK if the launcher was installed directly in the Python directory - IOW,
I'd think it OK if the PEP said "should be installed next to the
PythonXX.dll being installed" - but an important point in the above
working is the "already be on the system PATH" - ie, I don't really want
it put in a newly created directory unless the installer also adds that
directory to the PATH - and what to do on uninstall then becomes an issue.
One problem with all of this is uninstallation and specifically if the
user is uninstalling the most recent Python installation while leaving
earlier ones. I guess there are 2 general answers to this:
* The installer process could remember the previous association and
restore that on uninstall.
* We treat this as a "wont-fix" and document a work-around of asking the
user to reinstall the previous version to restore the file association.
We probably need to be mindful of adding too much extra work for the
installer process as that may well end up blocking us on getting this
into the next appropriate release. In particular, Martin's thoughts
here would be very useful.
This would force the user to reinstall that older one to re-establish
the associations correctly
BTW I thought of another thing that perhaps needs handling: what if a customized
command points to the launcher itself? It'd be turtles all the way down :-)
Yeah - I wonder if we can leverage the "job" api here and refuse to
start if there are already 2 processes in the job? OTOH, that is tricky
as it would also prevent someone using os.startfile with a .py file
From your second mail:
I've assumed that if a customised command is provided with arguments in the
shebang line, these will be ignored - if people want to run with different
options they can always define more customised commands. If you agree with this,
the PEP should probably explicitly state this.
I'm not too bothered to be honest - the customized commands exist purely
for alternative implementations, so my initial thoughts are that
additional args would be as useful for them as they are for cpython
invocations. IOW, if they don't need it, then CPython invocations don't
need it either, so maybe it can be dropped completely?
In a couple of cases I've implemented using fixed size arrays - for the lists of
installed Pythons and customised commands. Of course these can be made dynamic,
but what's there is good enough for the moment for exploration.
Sure - I think there is some policy that a Python version number will
never be > 10, so that sounds fine to me. So long as the launcher
doesn't blindly run off the end of such arrays I think it is fine -
limitations can be addressed in later versions.
It will be a few days until I can look at the implementation, but I'm
very happy to see it started. Given it is now ahead of the Python
reference impl, I wonder if we should just drop all wording about that
reference impl and just treat the C impl as canonical?
Cheers,
Mark
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