[help]How to load a class dynamic?

[dolephi9080]

Originally posted by Alex Martelli 
> dolephi9080 wrote:
>
> > Suppose I have some 3 party Modules, and In my program, I don't
>     know
> > what is the 3 party classes are, but I can find the name from
>     the 3
> > party's Module.
> > it provide a manifest, it has a line classname =
> > "mypackage.mymodule.MyClass"
> > now my program read this line, and how to instance the class
>     from
> > this string?
>
> In general, you cannot, because there is no information about what
> arguments you should pass for the instantiation.
>
> But let's assume you have that information from other sources, for
> example you know somehow that these classes should be instantiated
> by calling them without arguments.  So, your problem basically is
> reduced to getting the appropriate class object.
>
> In turn, that class object is an attribute of a module, so your
> problem reduces to getting that module.  Assuming 'mypackage' is
> on your sys.path (i.e. some directory of the sys.path has a
> subdirectory named 'mypackage' which contains a file __init__.py)
> then __import__ can do it -- otherwise you need to find out where
> the package is located, and you definitely do not have enough
> info for that in your specs.
>
> So basically we could have, just as clearly explained and
> exemplified in the Python online docs at
> http://www.python.org/doc/current/lib/built-in-funcs.html"]http-
> ://www.python.org/doc/current/lib/built-in-funcs.html[/url]
> (just prettied up a bit...):
>
> def my_import(structured_name):
>     mod = __import__(structured_name)
>     component_names = structured_name.split('.')
>     for component_name in component_names[1:]:
>         mod = getattr(mod, component_name)
>     return mod
>
> Now, my_import('mypackage.mymodule.MyClass') should give you
> the class object as the result.  Therefore,
>
> my_instance = my_import('mypackage.mymodule.MyClass')()
>
> [note the empty trailing parentheses to mean 'call without
> arguments'] should build and give you the instance you want,
> under the set of assumptions listed throughout this post.
>
>
> Alex 

It seems not work, I try it. it return a Module Object not class, so it
will tell you no module. it's main function is import Module not class

--
Posted via http://dbforums.com