Import module from a different subdirectory

[Peter J. Holzer]

On 2019-05-18 05:45:23 -0700, Rich Shepard wrote:
> On Sat, 18 May 2019, dieter wrote:
> > > > sys.path
> ['', '/home/rshepard/development/bustrac', '/usr/lib/python37.zip',
> '/usr/lib/python3.7', '/usr/lib/python3.7/lib-dynload',
> '/usr/lib/python3.7/site-packages']
> 
> All directories are present, and the one for the current project is the
> first one searched.
[...]
> I understand this. Within ~/development/bustrac as the CWD when I invoke the
> test application with the first line:
> 
> from classes import model as m
> 
> I still see this result:
> 
> $ python3 test_act_de.py Traceback (most recent call last):
>   File "test_act_de.py", line 1, in <module>
>     from classes import model as m
> ModuleNotFoundError: No module named 'classes'
> 
> 'classes' is a package (a subdirectory) containing an empty __init__.py, not
> a module. 'classes' conains a single module, model.py.

This works for me:

    hrunkner:~ 18:14 :-) 1141% cd tmp 
    hrunkner:~/tmp 18:14 :-) 1142% mkdir bustrac  
    hrunkner:~/tmp 18:14 :-) 1143% cd bustrac   
    hrunkner:~/tmp/bustrac 18:14 :-) 1144% mkdir classes 
    hrunkner:~/tmp/bustrac 18:14 :-) 1145% touch classes/__init__.py
    hrunkner:~/tmp/bustrac 18:14 :-) 1146% touch classes/model.py   
    hrunkner:~/tmp/bustrac 18:14 :-) 1147% python3
    Python 3.5.3 (default, Sep 27 2018, 17:25:39) 
    [GCC 6.3.0 20170516] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>> from classes import model
    >>> 

"" is in sys.path, so "classes" and classes.model are found.

Now lets go to a different subdirectory:

    hrunkner:~/tmp/bustrac 18:15 :-) 1148% mkdir scripts
    hrunkner:~/tmp/bustrac 18:15 :-) 1149% cd scripts 
    hrunkner:~/tmp/bustrac/scripts 18:15 :-) 1150% python3      
    Python 3.5.3 (default, Sep 27 2018, 17:25:39) 
    [GCC 6.3.0 20170516] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>> from classes import model
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ImportError: No module named 'classes'
    >>> 

This doesn't work, since there is no classes/model.py in "", only in "..".

But if I add a PYTHONPATH, it works again:

    hrunkner:~/tmp/bustrac/scripts 18:15 :-) 1151% export PYTHONPATH=~/tmp/bustrac
    hrunkner:~/tmp/bustrac/scripts 18:15 :-) 1152% python3                        
    Python 3.5.3 (default, Sep 27 2018, 17:25:39) 
    [GCC 6.3.0 20170516] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>> from classes import model
    >>> 


-- 
   _  | Peter J. Holzer    | we build much bigger, better disasters now
|_|_) |                    | because we have much more sophisticated
| |   | hjp at hjp.at         | management tools.
__/   | http://www.hjp.at/ | -- Ross Anderson <https://www.edge.org/>
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