Re: Writing func_closure?
Fernando Perez wrote: 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. def makeclosure(x): ... def _f(): ... x ... return _f.func_closure ... makeclosure(42) (cell at 0x4613bc: int object at 0x4a3e4c,) OK, that's kind of limited. God only knows what happens when there is more than one variable, although you could add extra levels of hackery to do with that. Many thanks though, I'll probably end up using a less dirty hack :) *Excellent* idea. -- Michael Hoffman -- http://mail.python.org/mailman/listinfo/python-list
Re: Writing func_closure?
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?
In [21]: def wrap(x):
: def f(y):
: return x+y
: return f
:
In [22]: f1=wrap('hello')
In [23]: f1.func_closure
Out[23]: (cell at 0x4168bcd4: str object at 0x41bc0080,)
My question is, how can I create one of these cell objects to stuff into the
closure (I want to do this from pure Python, not C extensions).
f1.func_closure[0].__class__()
Traceback (most recent call last):
File stdin, line 1, in ?
TypeError: cannot create 'cell' instances
Hmmm, that didn't work so well.
f1.func_closure = f1.func_closure
Traceback (most recent call last):
File stdin, line 1, in ?
TypeError: readonly attribute
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
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:
f1( there)\
'hello there'
_f2 = wrap(howdy)
f1 = new.function(f1.func_code, f1.func_globals, f1.func_name,
f1.func_defaults, _f2.func_closure)
f1( there)
'howdy there'
Mix-and-match functions! What will they think of next?
--
Michael Hoffman
--
http://mail.python.org/mailman/listinfo/python-list
Re: Writing func_closure?
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 -- http://mail.python.org/mailman/listinfo/python-list
Re: Writing func_closure?
Fernando Perez wrote: 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. As far as I know, there is currently no supported way of directly creating or modifying cell objects from Python; it can only be done by some obscure trickery. So the docs are telling the truth here, in a way. :-) -- Greg Ewing, Computer Science Dept, University of Canterbury, Christchurch, New Zealand http://www.cosc.canterbury.ac.nz/~greg -- http://mail.python.org/mailman/listinfo/python-list
Re: Writing func_closure?
Greg Ewing wrote: As far as I know, there is currently no supported way of directly creating or modifying cell objects from Python; it can only be done by some obscure trickery. So the docs are telling the truth here, in a way. :-) In a twisted, convoluted way :) But thanks for the clarification (which IMHO belongs in the docs). Oh well, it was a dirty hack anyways, so it's probably best not done. Cheers, f -- http://mail.python.org/mailman/listinfo/python-list
