[Tutor] import and reload in modules

[Kent Johnson]

Garry Willgoose wrote:
> In response to Kent's suggestion here is an updated post showing the  
> python code and the error log. The original reason for using try was  
> I thought maybe this was scoping problem and that maybe 2nd time  
> through the call it needed to import it again from scratch. As a side  
> observation for Kent I also tried replacing the exec on the import  
> statement with __init__('siberia900') and other variants using a text  
> variable and while they appeared to work I got a the following error
> 
>  >>> __import__('siberia900')
> <module 'siberia900' from 'siberia900.pyc'>
>  >>> siberia900.version
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> NameError: name 'siberia900' is not defined
> 
> Maybe its related don't know.

__import__() returns a value which is the imported module so you have to say
user_module = __import__('siberia900')
and then
reload(user_module)
user_module.version

> Anyway here's the original problem again with more info.

I think the problem is that the module is being imported in the scope of 
load(). The first time you run load(), a local name 'siberia900' is 
created and bound to the imported module. The second time you run 
load(), this name is not available and you get the name error.

One way to fix this would be to use a global dict as the namespace for 
the exec and eval calls. A better solution is to get rid of them 
entirely as I have suggested.

Kent

> 
> ---------------------------------
> current_model_name=''
> 
> def load():
>    global current_model_name
>    model='siberia900'
>    text1='import '+model
>    text2='reload('+model+')'
>    if model==current_model_name:
>      print 'here 1', text2
>      exec(text2)
>    else:
>      print 'here 10', text1
>      exec(text1)
>    current_model_name=model
>    version=eval(model+'.version')
>    return(version)
> ---------------------------------
>  >>> import mytest1
>  >>> mytest1.load()
> here 10 import siberia900
> '1.00'
>  >>> mytest1.load()
> here 1 reload(siberia900)
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
>    File "mytest1.py", line 10, in load
>      exec(text2)
>    File "<string>", line 1, in <module>
> NameError: name 'siberia900' is not defined
> ---------------------------------
> 
> 
> ====================================================================
> Prof Garry Willgoose,
> Australian Professorial Fellow in Environmental Engineering,
> Director, Centre for Climate Impact Management (C2IM),
> School of Engineering, The University of Newcastle,
> Callaghan, 2308
> Australia.
> 
> Phone: (International) +61 2 4921 6050 (Tues-Thurs); +61 2 6545 9574  
> (Fri-Mon)
> FAX: (International) +61 2 4921 6991 (Uni);
> Env. Engg. Secretary: (International) +61 2 4921 6042
> Centre WWW  :  www.c3im.org.au
> 
> email:  garry.willgoose at newcastle.edu.au
> email-for-life: garry.willgoose at alum.mit.edu
> ====================================================================
> "Do not go where the path may lead, go instead where there is no path  
> and leave a trail"
>                            Ralph Waldo Emerson
> ====================================================================
> 
> 
> 
> 
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