__metaclass__ and __author__ are already decorators

Paul Morrow pm_mon at yahoo.com
Sat Aug 21 20:46:29 CEST 2004


Leif K-Brooks wrote:

> Paul Morrow wrote:
> 
>> 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.  What is the compelling reason to invent a new one?  And if we 
>> do, what's to become of the old one?
>> <snip>
> 
> 
> I've thought about something along the lines of your suggestion before, 
> but it doesn't seem very Pythonic to assign special meaning to function 
> variables with special names to me. It's essentially a new syntax, but 
> disguised as an old syntax with an entirely different meaning.

We just need to stop thinking of them as local function variables. 
Instead we should think of __xxx__ attributes as describing the function 
itself (i.e. as a decorator would), as I believe that is almost always 
the author's intention when he/she uses such names inside of a 
function/method definition.  He wants to say something about the 
function (who wrote it, it's version, etc.), and is probably sad that it 
has the side-effect of creating a local variable.  So it probably 
shouldn't have that side-effect anymore.  It should create a function 
attribute instead (not to be confused with a local variable).

For classes, it's much easier to accept this new way of looking at 
__xxx__ attributes because it's consistent with our intention behind 
them (as names for metadata rather than normal, inheritable class 
attributes).






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