__import__ confusion

Leazen leazen at uol.com.ar
Wed Feb 26 15:50:08 CET 2003


Steven Taschuk wrote:
> Quoth Leazen:
> 
>>	I'm trying to load modules dinamically. All modules which define a
>>class (Plugin) should be imported and an object of the class within them
>>created, do you think using __import__ is the way to go or that I should
>>keep looking?
>>	Thanks again, first time doing this kind of thing.
> 
> 
> Hm.  Never done this sort of thing, but here's my first
> impressions, for what they're worth:
> 
> I assume you've got a plugins directory somewhere that your app
> knows about, and you want to spin through all the *.py files in
> that directory, loading each, and instantiating each module's
> Plugin class, if it defines one.  Is this correct?

Correct.

> If so, I'm not sure __import__ is best.  For one thing, I think
> it'll go wandering off on sys.path looking for the specified
> module; but you already know where the file is.  The facilities
> provided by the imp module might serve better.
> 
> Here's a quicky illustration.  (I hope those more familiar than I
> with this subject will offer comments.)
> 
> Two trivial plugin files:
> 
> [...]
> 
> Result:
>     $ python loader.py
>     Instantiating plugin from <module 'plugin1' from './plugin1.pyc'>
>     plugin1 instantiated
>     Instantiating plugin from <module 'plugin2' from './plugin2.pyc'>
>     plugin2 instantiated
>     No plugin in <module 'loader' from './loader.pyc'>
>     I'm plugin1!
>     I'm plugin2!
> 
> Seems to work, anyway.
> 
> Some caveats:
>     - The loader should look for *.pyc and *.pyo files too.  Maybe even
>       *.so files.
>     - The documentation says that imp.load_module() will do a reload if
>       the module has already been loaded; this might not be desirable.
>       I'm not sure how to prevent it, short of spinning through
>       sys.modules.
>     - The error handling is clumsy and probably wrong.
>     - There's no support for package structures in the plugin directory.

Thank you for this excelent reply!
	- '.so' files? As in shared libraries?
	- If the reloading is a problem I'll take care of that after it works.
I also thought about sys.modules.
	- I would need to load a package structure a node at a time. I think I
can use the module.__path__ attribute to get the path for each node.

Thanks again,
		Leazen










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