organizing your scripts, with plenty of re-use

Gabriel Genellina gagsl-py2 at yahoo.com.ar
Tue Oct 13 00:34:49 CEST 2009


En Mon, 12 Oct 2009 15:24:34 -0300, Buck <workitharder at gmail.com> escribió:

> On Oct 10, 9:44 am, "Gabriel Genellina" <gagsl-... at yahoo.com.ar>
> 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/
     +-- __init__.py
     +-- animals.py
     +-- mammals/
         +-- __init__.py
         +-- horse.py
         +-- otter.py
     +-- reptiles/
         +-- __init__.py
         +-- gator.py
         +-- newt.py
     +-- misc/
         +-- __init__.py
         +-- lungs.py
         +-- swimming.py


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).

-- 
Gabriel Genellina




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