Writing func_closure?

[Fernando Perez]

Michael Hoffman wrote:

> Fernando Perez wrote:
> 
>  > I am  trying to do a run-time modification of a function's closure,
>  > where I want to modify the value of one of the variables in the closure.
> 
> Out of curiosity, why?

Oh, I was just trying to play a little trick inside a tight loop where I would
modify on the fly the function's closure to change a parameter.  I can do it in
a million ways, but at creation time, the closure approach provides the
cleanest syntax.  But at runtime, I have an algorithm that needs to modify
certain parameters many times, and the least-expensive way would be to be able
to write directly into the closure.

> Closer inspection of the docs <http://docs.python.org/ref/types.html>
> reveals that it is not writable after all. Therefore the only way I can

Ah, the docs have improved.  I'm using 2.3.4, and the same page:

http://www.python.org/doc/2.3.4/ref/types.html

only says:

Of these, func_code, func_defaults, func_doc/__doc__, and func_dict/__dict__ may
be writable; the others can never be changed.

That's what led me to believe it could be done. Thanks for pointing me to the
2.4 docs, which are much less ambiguous.


> see to do it without writing an extension is to generate some dummy
> function and copy the func_closure attribute from it. Luckily, you have
> already produced a factory for such a function:

Yes, I knew of the new.function() approach, but the problem is that I don't know
how to make a fresh closure for it.  I can reuse the closure from a different
function, but the docs don't say how to make a valid closure tuple.  This is
the typical problem of the stdlib docs, which under-specify what is supposed to
go into a call and don't give at least a specific example.

Many thanks though, I'll probably end up using a less dirty hack :)

Cheers,

f