Problem with Dynamically unloading a module

[Jean-Michel Pichavant]

lordofcode wrote:
> Hi All
>
> Not an expert in Python, so sorry if this sounds like a silly
> question.
> I went through other few threads in the mailing list but they are not
> helping me much.
> I have run into a problem related to dynamically loading and unloading
> a module.
> I need to dynamically load a module and unload it and load another
> module.
>
> For example I have many files(All files in Python are modules right?)
> like mobile_1.py ,mobile_2.py, mobile_3.py  etc.. in my project folder
> which contains classes and methods with same name but different
> functionality.(am afraid I cannot change this structure as these files
> are generated randomly by the user)
>
> So initially when my program starts I have to load a default module. I
> do this as follows:
> ##############################
>   
>>> MODULE_name = "mobile_1"
>>> exec "from "+MODULE_name+" import *"
>>>       
> ##############################
> And use the methods defined in "mobile_1.py" file
>
> Now as the application continues , I may have to use the methods
> defined in "mobile_2.py" or "mobile_3.py" etc instead of the
> previously loaded module,which I incorrectly try to do as below:
> ####################
>   
>>> MODULE_name = "mobile_2"
>>> exec "from "+MODULE_name+" import *"
>>>       
> #####################
> The above import does not have any impact and the methods called from
> my application still pertain to mobile_1.py as its still in the
> current namespace(?).
> I tried below code with del(), reload() etc but could not figure it
> out.
> ###Code to unload a dll####
>   
>>> del sys.modules[MODULE_name]    #==> does not delete the reference in namespace
>>>       
>
>
> 1)How do I unload a module dynamically and completely remove the
> references in the module so a new module with same name references can
> be loaded?
> 2)Are there any alternative way to do the above requirement?
> Currently I am working around by restarting the whole initial setup
> for each new module which is unnecessary waste.Can I avoid this
> "reset"?
>
>   
1/ Do not use from x import *
2/ How many modules would you like to import in the end ? If this number 
is bound I would suggest to use a static approach:

import mod1
import mod2
import mod3
mod4 = __import__('mod4') # equivalent to import mod4

for mod in [mod1, mod2, mod3, mod4]:
    # will call func1 on each modules
    print "now using module %s functions " % mod.__file__
    mod.func1()
    mod.func2()

With this approach it's pretty much easy to call the correct 
methods/attributes, as every symbols is scopped by module namespace. You 
will have less hard time debugging your code.


3/ if you really need to unload the previous module, it's a little bit 
tedious.

import mod1
del mod1
sys.modules['mod1'] = None # will unload mod1 assuming mod1 was the only 
reference to that module.

But believe me, you don't want to mess up with the python import  mechanism.

JM