organizing your scripts, with plenty of re-use

Stef Mientki stef.mientki at
Tue Oct 13 01:15:02 CEST 2009

Gabriel Genellina wrote:
> En Mon, 12 Oct 2009 15:24:34 -0300, Buck <workitharder at> 
> escribió:
>> On Oct 10, 9:44 am, "Gabriel Genellina" <gagsl-... at>
>> wrote:
>>> The good thing is that, if the backend package is properly installed  
>>> somewhere in the Python path ... it still works with no modifications.
>> I'd like to get to zero-installation if possible. It's easy with
>> simple python scripts, why not packages too? I know the technical
>> reasons, but I haven't heard any practical reasons.
>> If the reasons are purely technical, it smells like a PEP to me.
> That's what I meant to say. It IS a zero-installation schema, and it 
> also works if you properly install the package. Quoting Steven 
> D'Aprano (changing names slightly):
> """You would benefit greatly from separating the interface from
> the backend. You should arrange matters so that the users see something
> like this:
> project/
> +-- animal
> +-- mammal
> +-- reptile
> +-- somepackagename/
>     +--
>     +--
>     +-- mammals/
>         +--
>         +--
>         +--
>     +-- reptiles/
>         +--
>         +--
>         +--
>     +-- misc/
>         +--
>         +--
>         +--
> where the front end is made up of three scripts "animal", "mammal" and
> "reptile", and the entire backend is in a package.""" [ignore the rest]
> By example, the `animal` script would contain:
> from somepackagename import animals
> animals.main()
> or perhaps something more elaborate, but in any case, the script 
> imports whatever it needs from the `somepackagename` package.
> The above script can be run:
> a) directly from the `project` directory; this could be a checked out 
> copy from svn, or a tar file extracted in /tmp, or whatever. No need 
> to install anything, it just works.
> b) alternatively, you may install somepackagename into site-packages 
> (or the user site directory, or any other location along the Python 
> path), and copy the scripts into /usr/bin (or any other location along 
> the system PATH), and it still works.
> The key is to put all the core functionality into a package, and place 
> the package where Python can find it. Also, it's a good idea to use 
> relative imports from inside the package. There is no need to juggle 
> with sys.path nor even set PYTHONPATH nor import __main__ nor play any 
> strange games; it Just Works (tm).
please don't get angry,
I'm not a programmer, I'm just a human ;-)

Hierarchical choices are done on todays knowledge, tomorrow we might 
have different views and want/need to arrange things in another way.
An otter may become a reptile ;-)
So from the human viewpoint the following should be possible (and is for 
example possible in Delphi)
- I can move the complete project anywhere I like and it should still 
work without any modifications (when I move my desk I can still do my work)
- I can move any file in he project to any other place in the project 
and again everything should work without any modifications ( when I 
rearrange my books, I can still find a specific book)

In my humble opinion if these actions are not possible, there must be 
redundant information in the collection. The only valid reason for 
redundant information is to perform self healing (or call it error 
correction), and here we have a catch-22.

Stef Mientki

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