[Jython-dev] shebang controlled python launcher.

[Vernon C. <ver...@gm...>]

Hello, all.
  You don't know me, I just signed up to the group.  I am being
required to learn Java for a college class [Bill Gates and I dropped
out the same year & I am now back] and I added the Python support
package to NetBeans -- since Python has been my language of choice for
several years.  I was very impressed with Jython 2.5.  I dredged up an
old program which I wrote several years ago as an adjunct to a Java
desktop application. The Python implementation I was using had gone
away (I had "borrowed" the Python from inside OpenOffice) so my little
application had quit working. It seemed that simply running my old
code in Jython would do the trick.  It tested fine in NetBeans.
  Then I started trying to learn how to run it from a shortcut.  Yipes!

A few days ago a discussion cropped on the IronPython discussion list
about how to automatically detect which version of Python to use for a
particular script.  I suggested that the POSIX practice of the first
line containing "#!/usr/bin/yourPythonVerlsionHere" would be
reasonable.  Micheal Foord informed us that that idea was already in
process.

In a later message I suggested that the same method they talked about
could also be adapted to start up a Jython script.  I include the
latest exchange...
v v v v v v
On 16/03/2011 3:43 PM Mark Hammond wrote:

On 16/03/2011 1:28 AM, Michael Foord wrote:
>
> On 15/03/2011 07:18, Vernon Cole wrote:
>>
>> #!/usr/bin/ipy3

...

> There has been a long discussion recently on Python-dev [1] suggesting
> the creation of exactly such a launcher program for Python on Windows.
> Mark Hammond (copied) said he would implement it. Including IronPython
> support is a fine idea.

I've made a start on this.  I've a 'reference implementation' in
Python and am starting a PEP which I hope to post to python-dev in the
next week or so (but please let me know if you would like to have a
look at it before then).

While I've been focusing on CPython, other implementations could be
supported so long as this "launcher" could reliably locate them.  For
example, a shebang line of "/usr/bin/python2.6" could use the registry
to locate the Python 2.6 implementation and execute it.  If the
shebang line specifies just "/usr/bin/python", then exactly how to
determine which version to use is still up for grabs and as python-dev
is never short of opinions <wink> I figured I'd leave that level of
detail until there is more public discussion.

If there is a reliable way to locate an IronPython implementation
given just its version number, then the same basic scheme could
certainly be used for IronPython or jython - but I'd be keen to have
someone from those communities help with that side of things.

The intention is that the final implementation would be written in C
and be distributed with CPython, but that would depend on the support
of python-dev for this scheme.  However, that raises the question of
how IronPython etc would actually get this launcher installed assuming
no CPython installation exists.  This too would need some feedback
from the communities.

Hope this is useful...

Cheers,

Mark
^ ^ ^ ^ ^ ^ ^

So I am approaching your group to see if there is interest in getting
in on this.  I have asked Mark for a copy of his code. I will try to
adapt it to include IronPython -- and Jython if you all are interested
and will feed me some correct skeleton code to use.
--
Vernon Cole