On 06/07/2012 10:08 AM, Eric Snow wrote:
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.
I doubt there are any but corner cases to demonstrate here. I'd don't
presume to say what use there may be in changing a function's state.
However, the fact is that a change to any of the following would cause
a cached __signature__ to be out of sync:
* f.__annotations__
* f.__closure__
* f.__code__
[... other dunder attributes elided ...]
In other words: this is possible but extremely unlikely, and will only
be done knowingly and with deliberate intent by a skilled practitioner.
I think it's reasonable to declare that, if you're monkeying around with
dunder attributes on a function, it's up to you to clear the
f.__signature__ cache if it's set. Like Spiderman's uncle Cliff
Robertson said: with great power comes great responsibility.
I am now firmly in the "using __signature__ as a cache is fine, don't
make copies for no reason" camp.
//arry/
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