problem pickling a function

[Calvin Spealman]

On Dec 12, 2007, at 11:01 AM, Emin.shopper Martinian.shopper wrote:

> Dear Experts,
>
> I love the pickle module, but I occasionally have problems pickling  
> a function. For example, if I create an instance g of class f and  
> assign g.x to a function, then I cannot pickle g (example code  
> below). I know that I can pickle f separately if I want to, and I  
> understand why I get the pickling error.

This all has to do with how pickles are able to recreate the objects  
in question. Pickle can only handle things, basically, with global  
names. This pretty much means it can handle regular classes and  
module functions, but not the methods of those classes. Why? Why  
would it have to? If it can handle the class it just expects that  
name to be the same class when it brings it back up, it doesn't  
actually store the class or function itself, just the name.

> But is there a way to assign functions to instances of a class  
> without preventing pickleability? It doesn't seem unreasonable to  
> me to want to assign functions to instances of a class (after all  
> functions are first class objects, so why shouldn't I be able to  
> pass them around?) Is there a better way or is this just a  
> limitation of pickle?

Presumably you could do something with __getstate__ and __setstate__  
methods, but this is many cases of "Are you really sure you want to  
do that?"