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To: python-list@python.org
From: Peter Otten <__peter__@web.de>
Subject: Re: changing sys.path
Date: Fri, 10 Feb 2012 16:27:24 +0100
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Andrea Crotti wrote:

> Ok now it's getting really confusing, I tried a small example to see
> what is the real behaviour,
> so I created some package namespaces (where the __init__.py declare the
> namespace package).
> 
>    /home/andrea/test_ns:
>    total used in directory 12 available 5655372
>    drwxr-xr-x 3 andrea andrea 4096 Feb 10 14:46 a.b
>    drwxr-xr-x 3 andrea andrea 4096 Feb 10 14:46 a.c
>    -rw-r--r-- 1 andrea andrea  125 Feb 10 14:46 test.py
> 
>    /home/andrea/test_ns/a.b:
>    total 8
>    drwxr-xr-x 3 andrea andrea 4096 Feb 10 14:47 a
>    -rw-r--r-- 1 andrea andrea   56 Feb 10 14:35 __init__.py
> 
>    /home/andrea/test_ns/a.b/a:
>    total 8
>    drwxr-xr-x 2 andrea andrea 4096 Feb 10 14:47 b
>    -rw-r--r-- 1 andrea andrea   56 Feb 10 14:35 __init__.py
> 
>    /home/andrea/test_ns/a.b/a/b:
>    total 12
>    -rw-r--r-- 1 andrea andrea  25 Feb 10 14:36 api.py
>    -rw-r--r-- 1 andrea andrea 153 Feb 10 14:37 api.pyc
>    -rw-r--r-- 1 andrea andrea  56 Feb 10 14:35 __init__.py
> 
>    /home/andrea/test_ns/a.c:
>    total 8
>    drwxr-xr-x 3 andrea andrea 4096 Feb 10 14:47 a
>    -rw-r--r-- 1 andrea andrea   56 Feb 10 14:35 __init__.py
> 
>    /home/andrea/test_ns/a.c/a:
>    total 8
>    drwxr-xr-x 2 andrea andrea 4096 Feb 10 14:47 c
>    -rw-r--r-- 1 andrea andrea   56 Feb 10 14:35 __init__.py
> 
>    /home/andrea/test_ns/a.c/a/c:
>    total 12
>    -rw-r--r-- 1 andrea andrea  20 Feb 10 14:36 api.py
>    -rw-r--r-- 1 andrea andrea 148 Feb 10 14:38 api.pyc
>    -rw-r--r-- 1 andrea andrea  56 Feb 10 14:35 __init__.py
> 
> 
> So this test.py works perfectly:
> import sys
> sys.path.insert(0, 'a.c')
> sys.path.insert(0, 'a.b')
> 
> from a.b import api as api_ab
> 
> from a.c import api as api_ac
> 
> While just mixing the order:
> import sys
> sys.path.insert(0, 'a.b')
> 
> from a.b import api as api_ab
> 
> sys.path.insert(0, 'a.c')
> from a.c import api as api_ac
> 
> Doesn't work anymore
> 
> [andrea@precision test_ns]$ python2 test.py
> Traceback (most recent call last):
>    File "test.py", line 7, in <module>
>      from a.c import api as api_ac
> ImportError: No module named c
> 
> 
> 
> Am I missing something/doing something stupid?

The package a will be either a.c/a/ or a.b/a/ depending on whether a.c/ or 
a.b/ appears first in sys.path.

If it's  a.c/a, that does not contain a c submodule or subpackage.