Python Global Variable: sharing between function class then function

Question

I'm trying to get the following global variable storage_i to be accessible to the lvl1 function, I have been able to pass it to other functions inside of the class birdofprey but I can't get it outside of that framework. I have looked around at using global variables between functions, etc, and I have also seen global var usage discouraged. But, basically I am trying to have the value of storage_i summed up from all the threads. So if that could be done without a global variable that would also be great. Any help would be appreciated.

The Code: https://github.com/eWizardII/homobabel/blob/master/Experimental/demo_async_falcon.py

Dan Breslau · Accepted Answer · 2010-12-05 06:54:12Z

1

Replace this:

global storage_i
storage_i = i

With this:

birdofprey.storage_i = i

You also have a typo at line 75:

storage_ii = stroage_i + storage_ii

(stroage_i was intended to be storage_i)

This line should actually be:

storage_ii =  birdofprey.storage_i + storage_ii

EDIT: Also, without having looked closely at it, your use of a class attribute (storage_i) looks like it's susceptible to race conditions. Consider using mutexes to guard accesses to that attribute. I think you also need to wait for the threads to finish executing before you can access the values.

But I'm not sure if a global (or class attribute) is really what you want. I think what you really want is a thread-local variable that you can access after the thread has finished (see the Thread.join method.) If I'm reading that correctly, then forget what I wrote above about mutexes. Instead, set the storage_i attribute as self.storage_i (creating a separate instance for each thread.) Then in the for loop where you're summing the values, access the value as urlv.storage_i. Again, it looks like it's important that you perform a join on each thread before you try to access its values.

That's all the help I can offer for now; perhaps tomorrow morning (my time) I can check in again.

edited Dec 5, 2010 at 6:54

answered Dec 5, 2010 at 6:29

Dan Breslau

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5 Comments

eWizardII Over a year ago

Thanks, I set that up however I think urlv.storage_i doesn't work, currently I tried urlv.self, etc, still looking into what else might fix it since it claims that AttributeError: 'birdofprey' object has no attribute 'storage_i' Code: github.com/eWizardII/homobabel/blob/master/Experimental/… (you can ignore that it says urlvself atm I was just testing different things)

eWizardII Over a year ago

The issue seems to be that I can access variables that are under the function run, but I can access those under the class birdofprey.

eWizardII Over a year ago

Okay so I was able to get it to work, I needed to use locking on the threads it seems, though I'll try it later without locking, but for now it works this way. Thanks. Code: github.com/eWizardII/homobabel/blob/master/Experimental/…

eWizardII Over a year ago

Or rather, the locking make it work, but that means that there aren't multiple threads running anymore since the second thread is waiting on the first.

eWizardII Over a year ago

So basically fixed the issue with summing the numbers, now new problem about only two threads are running. stackoverflow.com/questions/4360636/…

Bill the Lizard · Accepted Answer · 2012-03-08 13:41:18Z

0

If you want to access storage_i under lvl1() then use:

birdofprey.storage_i

Well storage_i is not a global variable, its a class attribute.

edited Mar 8, 2012 at 13:41

Bill the Lizard

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answered Dec 5, 2010 at 6:11

Shiv Deepak

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5 Comments

eWizardII Over a year ago

Okay thanks, but then how do I get access to it when it's set to i under def run(self): ?

Shiv Deepak Over a year ago

don't use global storage_i, you have to access it using self.storage_i

eWizardII Over a year ago

Okay, when I set it to just store as @storage_i = i@ in the function and access it under @lvl1()@ with @storage_ii = birdofprey.self.storage_i + storage_ii@ it claims that - type object 'birdofprey' has no attribute 'self' Code: github.com/eWizardII/homobabel/blob/master/Experimental/…

Dan Breslau Over a year ago

You removed the definition of storage_i that you'd had in the lvl1() function. (I think it was simply: storage_i = 0) Without that, then indeed there is no storage_i attribute. Also, you don't need self. Just birdofprey.storage_i works.

eWizardII Over a year ago

Okay, I made those corrections, however it just prints 0's. Code: github.com/eWizardII/homobabel/blob/master/Experimental/…

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