[Python-Dev] Import semantics

Samuele Pedroni pedronis at strakt.com
Mon Jun 12 10:00:13 CEST 2006

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 

This is unlikely to change for backward compatibility reasons, at least 
from my POV.

> Thanks,
> Fabio
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