[Python-Dev] __metaclass__ and __author__ are already decorators

[Phillip J. Eby]

At 12:29 PM 8/21/04 -0400, Paul Morrow wrote:
>[I posted this on comp.lang.python.general but I'm not sure how many of 
>the folks here read that newsgroup, so my apologies if you're seeing this 
>twice.]
>
>Thinking about decorators, and looking at what we are already doing in our 
>Python code, it seems that __metaclass__, __author__, __version__, etc. 
>are all examples of decorators.  So we already have a decorator syntax.

The items you describe are not decorators, they are attributes.  The 
current syntax for decorators is 'x = decorator(x)'.


>         def baz(self, a, b):
>             """ This describes the baz method. """
>             __synchronized__ = True
>             __returns__ = None
>             __author__ = 'Neville Shunt'
>             # body of baz goes here...

This syntax already has a different and conflicting meaning in today's 
Python.  A different such syntax:

     [synchronized(), returns(None), author("Neville Shunt")]
     def baz(self, a, b):
         """ This describes the baz method. """
         # body of baz goes here...

has already been rejected on the basis that this too has meaning in today's 
Python, and that the syntax produces "spooky action at a distance".  That 
is, it's "magical" that the function calls affect the definition below.

Following this logic, expecting assignments to magic names contained within 
a function's body to magically invoke decorator functions with different 
names *before and outside the block* where those names are assigned to in 
the code, seems far less likely to be considered acceptable.