How to organize source code and "import"s???

[John Roth]

"Tian" <wangtianthu at gmail.com> wrote in message 
news:1111982658.540250.113310 at z14g2000cwz.googlegroups.com...
>I am writing a python program which needs to support some plug-ins. I
> have an XML file storing some dynamic structures. XML file records some
> class names whose instance needs to be created in the run time while
> parsing the XML file. I wonder what is the best solution for this
> problem?
>
> I also have some problem about the "import". How should I design my
> packages?
> Say, I have all code locates at c:\projects\sami, "c:\project" is in my
> PYTHONPATH environment variable. Suppose my folder structure is like
> this:
>
> c:
> projects\             <-----this directory is in PYTHONPATH
>          sami\
>                 __init__.py
>                 main.py
>                 xmlparser.py
>                 window.py
>                 proc.py
>                 support\
>                          __init__.py
>                          helper.py
>                 plugins\
>                          __init__.py
>                          BaseClass.py    <---no instance for this one
>                          ExtClassA.py
>                          ExtClassB.py
>                          ExtClassC.py
>                          ExtClassD.py
>
>
>
> Each file in \projects\sami\plugins contains a class with a same name
> as the file, (ExtClassA.py has class ExtClassA), the instance of these
> classes need to be created at runtime while functions in xmlparser.py
> is parsing an XML file. main.py is the start point of the program.

The solution to most dynamic import issues lies in the __import__()
function, which is the very first function documented in the built-in
functions page.

I've found that keeping it as simple as possible helps a lot. Just load
the module, get the address of the top level module from the __import()__
function, and use getattr() to trace down the chain of modules to the
class you want to access.

> Other files in the \projects\sami\ and projects\sami\support are
> supporting modules.
>
> 1. What should I write in each __init__.py ???f

Nothing.

>   In "main.py", if I need functions in "proc.py", should I write
> "import proc"?  If I need functions in "helper.py", can i write "import
> support.helper"?? what else should I do to support all these?

If you know you're going to need something, just import it.
There's no need to get fancy unless you've got import loops.
Then you need to break them and do the other accesses dynamically
after the modules have finished loading.

> 2. What is the best way to make instance of a class from a string type
> name? One method I have successfully tried is using "from SomeWhere
> import *", then get class from globals() and make instance.

Use the getattr() function.

> But How can
> I import all "ExtClass?.py"? Where should I write these import codes?

If you want to import all the names in a module, look in the module's
__dict__. That's not recommended, however.

If you want to import all the modules in a directory, then you need to
read the directory (see the os module) and import them individually.

John Roth


>