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.
Other files in the \projects\sami\ and projects\sami\support are supporting modules.
1. What should I write in each __init__.py ???
If I understand your intent correctly here, you shouldn't need anything in any of them.
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"??
No, you should use absolute imports and write: import sami.proc import sami.support.helper or perhaps import sami.proc as samiproc import sami.support.helper as samihelper
2. What is the best way to make instance of a class from a string type name?
Why do you expect to need to do this? Usually you can just import the class's module directly and then use getattr, e.g.:
py> modules = [__import__('sami.plugins.%s' % filename[:-3],
... globals(), locals(), ['ExtClass'])
... for filename in os.listdir('sami/plugins')
... if filename.endswith('.py')
... and filename not in ['BaseClass.py', '__init__.py']]
py> modules
[<module 'sami.plugins.ExtClassA' from 'D:\Steve\sami\plugins\ExtClassA.py'>,
<module 'sami.plugins.ExtClassB' from 'D:\Steve\sami\plugins\ExtClassB.py'>]
py> modules[0]
<module 'sami.plugins.ExtClassA' from 'D:\Steve\sami\plugins\ExtClassA.py'>
py> modules[0].ExtClass
<class 'sami.plugins.ExtClassA.ExtClass'>
py> getattr(modules[0], 'ExtClass')
<class 'sami.plugins.ExtClassA.ExtClass'>
See the documentation for __import__ for more details[1].
But How can I import all "ExtClass?.py"?
I would do this as above, using __import__.
STeVe
[1] http://docs.python.org/lib/built-in-funcs.html -- http://mail.python.org/mailman/listinfo/python-list
