What should a decorator do if an attribute already exists?

[Peter Otten]

Steven D'Aprano wrote:

> I have a decorator that adds an attribute to the decorated function:
> 
> 
> def decorate(func):
>     instrument = make_instrument()
> 
>     @functools.wraps(func)
>     def inner(*args):
>         instrument.start()
>         result = func(*args)
>         instrument.finish()
>         return result
> 
>    inner.instrument = instrument
>    return inner
> 
> 
> The actual nature of the instrumentation isn't important: depending on the
> decorator, it might count the number of function calls made, how long it
> takes, count cache hits, or something else.
> 
> My question is, what should I do if the decorated function already has an
> instrument attribute?
> 
> 1. raise an exception?
> 
> 2. raise a warning, and over-write the attribute?
> 3. raise a warning, and skip adding the attribute?
> 4. raise a warning, and rename the existing instrument to
>    something else before writing my own instrument?
> 
> 5. silently over-write the attribute?
> 
> 
> I think 5 is clearly wrong, 4 is too difficult, and 3 seems pointless. So
> I think either 1 or 2 is the right thing to do.
> 
> Thoughts?

Silently overwrite it. For

@decorate
@decorate
def f():
    pass

the original instrument is still accessible as f.__wrapped__.instrument, so 
5 is the easy way to get 4.