Weird interaction with nested functions inside a decorator-producing function and closuring of outer data...

Adam Jorgensen adam.jorgensen.za at gmail.com
Wed Aug 24 16:30:13 CEST 2011


Thanks :-) Sorry about the size, I wasn't sure what was relevant...

On 24 August 2011 15:29, Peter Otten <__peter__ at web.de> wrote:
> Adam Jorgensen wrote:
>
>> Hi all, I'm experiencing a weird issue with closuring of parameters
>> and some nested functions I have inside two functions that
>> return decorators. I think it's best illustrated with the actual code:
>
> You should have made an effort to reduce its size
>> # This decorator doesn't work. For some reason python refuses to
>> closure the *decode_args parameter into the scope of the nested
>> decorate and decorate_with_rest_wrapper functions
>> # Renaming *decode_args has no effect
>> def rest_wrapper(*decode_args, **deco_kwargs):
>>     def decorate(func):
>>         argspec = getfullargspec(func)
>>         decode_args = [argspec.args.index(decode_arg) for decode_arg
>> in decode_args]
>
> I didn't read the whole thing, but:
>
>>>> def f(a):
> ...     def g():
> ...             a = a + 42
> ...             return a
> ...     return g
> ...
>>>> f(1)()
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
>  File "<stdin>", line 3, in g
> UnboundLocalError: local variable 'a' referenced before assignment
>
> Python treats variables as local if you assign a value to them anywhere in
> the function. The fix is easy, just use another name:
>
>>>> def f(a):
> ...     def g():
> ...             b = a + 42
> ...             return b
> ...     return g
> ...
>>>> f(1)()
> 43
>
> In Python 3 you can also use the nonlocal statement.
>
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>



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