[Python-ideas] make __closure__ writable
andrew.svetlov at gmail.com
Thu Mar 22 21:56:30 CET 2012
>From my perspective Yury's patch is simple and clean.
Hi described very well why decorators (which often implemented as
functions which own __closure__) cannot be easy patched.
While overriding __closure__ is not common case it's hard to do that
if you really need.
If __code__ is already writable there are no reason to prevent writing
to __closure__ as well.
I am +1 to push the patch in 3.3.
On Tue, Mar 20, 2012 at 4:59 PM, Yury Selivanov <yselivanov.ml at gmail.com> wrote:
> On 2012-03-20, at 10:56 AM, Yury Selivanov wrote:
>> Because usually you write decorators as functions, not classes. And
>> when you do the former style, you usually do it in the following way:
>> def decorator(func):
>> def wrapper(*args, **kwargs):
>> return func(*args, **kwargs)
>> functools.wraps(wrapper, func)
>> return wrapper
>> Now, let's use it:
>> def some_func(): pass
>> OK. At this point, 'some_func' object has a '__wrapped__' attribute,
>> that points to original 'some_func' function. But whatever you write
>> to 'some_func.__wrapped__' won't change anything, as the 'wrapper'
>> will continue to call old 'some_func'. Instead of assigning something
>> to __wrapped__, we need to change it in-place, by doing
>> '__wrapped__.__closure__ = new_closure'.
> And as I told you in the first example: there is no problem when you have
> only one decorator. You can surely just return a new FunctionType().
> But when you have many of them, such as:
> def some_func(): pass
> The only way to modify the __closure__ it to write to the __wrapped__
> attribute of 'decorator1' wrapper.
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