user modules

[Cameron Walsh]

Tuomas wrote:
> Cameron Walsh wrote:
>> Hi,
>>
>> I'm writing a python program to analyse and export volumetric data.  
>> To make development and extension easier, and to make it more useful 
>> to the public when it is released (LGPL), I would like to enable users 
>> to place their own python files in a "user_extensions" directory.  
>> These files would implement a common interface in order for the main 
>> program to be able to read them and execute the necessary code.
>>
>> My question is what is the best way of implementing this?
>>
>> I have investigated importing them as modules, but unless the user 
>> modifies the main program I cannot see how the main program can learn 
>> of the existence of specific modules.
>>
>> For example:
>>
>> from user_modules import *
>> # directory 'user_modules' contains __init__.py allowing this
>> # From here I would need a list of the imported modules, in order to
>> # execute a common command on each of them, such as
>>
>> for module in imported_modules:
>>     module.initialise()
>>     module.get_tab_window()
>>
>>
>> How do I get from the first bit to the second bit, or is there a 
>> better way of obtaining the functionality I need?
>>
>>
>> --Cameron.
> 
> import os
> 
> files=os.listdir('user_modules')
> tabs=[]
> for fle in files:
>     if fle.endswith('.py'):
>         module=__import__(fle[0:-3], 'user_modules', None,
>                ['initialise', 'get_tab_window'])
>         module.initialise()
>         tabs.append(module.get_tab_window())
> 
> *not tested*
> 
> print __import__.__doc__
> __import__(name, globals, locals, fromlist) -> module
> 
> Import a module.  The globals are only used to determine the context;
> they are not modified.  The locals are currently unused.  The fromlist
> should be a list of names to emulate ``from name import ...'', or an
> empty list to emulate ``import name''.
> When importing a module from a package, note that __import__('A.B', ...)
> returns package A when fromlist is empty, but its submodule B when
> fromlist is not empty.
> 
> Tuomas
> 

Thanks Tuomas, your solution worked a charm, with two changes:
1.)  Check I'm not trying to import __init__.py
2.)  module=__import__(fle[0:-3], 'user_modules', None,
                ['initialise', 'get_tab_window'])
      had to be changed to:
      module=__import__("user_modules.%s" %fle[0:-3], None, None,
                ['initialise', 'get_tab_window'])

For some reason it wasn't setting the context properly, I'll have to 
learn more about the function.

Thanks for teaching me how to read the documentation properly, about how 
private keywords like "import" are defined, and for providing a solution 
to a problem I'm likely to face many more times.

Best regards,

Cameron.