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Date: Thu, 08 Dec 2011 14:47:00 +0100
From: Bastien Semene <bsemene@cyanide-studio.com>
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CC: python-list@python.org
Subject: Re: sending a variable to an imported module
References: <4EE09F55.2050504@cyanide-studio.com> <4EE0AA5E.8000005@davea.name>
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:16826

Thanks both,

Putting the variable inside a module works well.
As the content is an object created inside another module I'm using this 
trick :

    module.CONFIG = module.load()

So the variable is handled by the module that creates/use it, easy to 
use and pretty "native" to understand.

Le 08/12/2011 13:15, Dave Angel a écrit :
> On 12/08/2011 06:28 AM, Bastien Semene wrote:
>> Hi list,
>>
>> I'm trying to pass a variable to an imported module without singletons.
>> I've seen in the doc, and tested that I can't use global to do it :
>>
>> === module.py ===
>> def testf():
>>  print test
>>
>>
>> === main.py ===
>> global test
>> test = 1
>>
>> imported_module = __import__(module, globals(), locals(), [], -1)
>>
>> importmodule.testf()
>>
>> === output ===
>> NameError: global name 'test' is not defined
>>
>>
> Please paste your code and your stacktrace, don't retype them.  In the 
> above, you spelled 'imported_module" two different ways, and forgot 
> the quotes around "modue", so it couldn't run.  There are probably 
> other problems, but what's the point?
>>
>> While I was reading many (many) threads about singleton I read people 
>> claiming that singletons can always be avoided (I can't remeber the 
>> most relevant thread on stackoverflow).
>> I don't want to start a new debate about singletons, I think Internet 
>> has enough debates yet.
>>
>> But in my case I'd like to access this variable anywhere and at 
>> anytime without having to pass it as a parameter everywhere (this 
>> variable is a configuration manager object).
>> How can I achieve that without singletons ?
>> I'm beginner in Python, that's why I'm maybe missing something obvious.
> global variables are global only within their own module, but you 
> probably knew that.
>
> And using the global keyword in main.py isn't accomplishing anything.  
> Since you're not inside a def or a class, test is already global, as 
> soon as you give it a value.
>
> You don't pass values to a module, you load the module.  And if the 
> module doesn't have any top-level code, you can "monkey-patch" it to 
> your heart's content, on lines following.
>
> If mymodule.py doesn't have a global value test, and you wish it did, 
> you can simply do something like:
> import  mymodule
> mymodule.test = 42
> This attribute of mymodule is totally unrelated to one of the same 
> name in main.py.  if you want to refer to it, or to change it again, 
> from main.py, you'd have to use  mymodule.test.
>
> If the module had top-level code that needed to see your new global, 
> then you'd have a problem, because you can't put it there till after 
> the import returns.
>
> Now, most of the time when this sort of thing happens, what you really 
> want is to define another module whose only purpose is to supply these 
> common values.  That module should get imported by both your script 
> and your module.
>
>