[Python-Dev] Import semantics

[Guido van Rossum]

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/)