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Thu Jun 7 16:12:43 CEST 2012 · https://mail.python.org/pipermail/python-dev/2012-June/120035.html

On 06/06/2012 06:00 PM, Nick Coghlan wrote:
> On Thu, Jun 7, 2012 at 10:52 AM, Eric Snow<ericsnowcurrently at gmail.com>  wrote:
>> Furthermore, using __signature__ as a cache may even cause problems.
>> If the Signature object is cached then any changes to the function
>> will not be reflected in the Signature object.  Certainly that's an
>> unlikely case, but it is a real case. [...]
> +1

I'm missing something here.  Can you give me an example of modifying an 
existing function object such that its Signature would change?  
Decorators implementing a closure with a different signature don't 
count--they return a new function object.

> Providing a defined mechanism to declare a public signature is good,
> but using that mechanism for implicit caching seems like a
> questionable idea. Even when it *is* cached, I'd be happier if
> inspect.signature() returned a copy rather than a direct reference to
> the original.

I'll say this: if we're going down this road of "don't cache Signature 
objects", then in the case of __signature__ we should definitely return 
a copy just for consistency's sakes.  It'd be a miserable implementation 
if signature() sometimes returned the same object and sometimes returned 
different but equivalent objects when called multiple times on the same 
object.

//arry/
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Showing content from https://mail.python.org/pipermail/python-dev/2012-June/120035.html below:

[Python-Dev] Updated PEP 362 (Function Signature Object)