[Python-Dev] Import semantics

[Frank Wierzbicki]

Sorry for the untrimmed conversation, but I've cc'ed jython-dev, my
comments are at the bottom.

On 6/12/06, Guido van Rossum <guido at python.org> wrote:
> On 6/12/06, Samuele Pedroni <pedronis at strakt.com> wrote:
> > Fabio Zadrozny wrote:
> > > Python and Jython import semantics differ on how sub-packages should be
> > > accessed after importing some module:
> > >
> > > Jython 2.1 on java1.5.0 (JIT: null)
> > > Type "copyright", "credits" or "license" for more information.
> > >  >>> import xml
> > >  >>> xml.dom
> > > <module xml.dom at 10340434>
> > >
> > > Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310 32 bit (Intel)] on
> > > win32
> > > Type "help", "copyright", "credits" or "license" for more information.
> > >  >>> import xml
> > >  >>> xml.dom
> > > Traceback (most recent call last):
> > >   File "<stdin>", line 1, in ?
> > > AttributeError: 'module' object has no attribute 'dom'
> > >  >>> from xml.dom import pulldom
> > >  >>> xml.dom
> > > <module 'xml.dom' from 'C:\bin\Python24\lib\xml\dom\__init__.pyc'>
> > >
> > > Note that in Jython importing a module makes all subpackages beneath it
> > > available, whereas in python, only the tokens available in __init__.py
> > > are accessible, but if you do load the module later even if not getting
> > > it directly into the namespace, it gets accessible too -- this seems
> > > more like something unexpected to me -- I would expect it to be
> > > available only if I did some "import xml.dom" at some point.
> > >
> > > My problem is that in Pydev, in static analysis, I would only get the
> > > tokens available for actually imported modules, but that's not true for
> > > Jython, and I'm not sure if the current behaviour in Python was expected.
> > >
> > > So... which would be the right semantics for this?
> >
> > the difference in Jython is deliberate. I think the reason was to mimic
> > more the Java style for this, in java fully qualified names always work.
> > In jython importing the top level packages is enough to get a similar
> > effect.
> >
> > This is unlikely to change for backward compatibility reasons, at least
> > from my POV.
>
> IMO it should do this only if the imported module is really a Java
> package. If it's a Python package it should stick to python semantics
> if possible.
>
> --
> --Guido van Rossum (home page: http://www.python.org/~guido/)

This is a tough one since the BDFL and Samuele disagree here.  Perhaps
we should document the Java import behavior as permanent, but document
the Python imports in Jython as being deprecated but available until
some future release?  I believe we would keep it at least through
Jython 2.3.

-Frank