[Python-Dev] FW: [Python-checkins] python/nondist/peps pep-0318.txt, 1.25, 1.26

[Raymond Hettinger]

> List some possible reasons why arriving at consensus about 
> decorators has been so hard (or impossible) to achieve

Thanks.  I think that was an important contribution to the discussion.
At this point, looking at the meta-discussion is likely to best way to
help cut through the current morass.



+There is no one clear reason why this should be so, but a
+few problems seem to be most problematic.

A possible social issue is that decorators can be used in a tremendous
variety of ways, each of which is only needed or appreciated by small,
disjoint groups of users.  For instance, applications to ctypes have
unique needs that not understood or shared by others. Some users want to
use decorators for metaclass magic that scares the socks off of the
rest.


> +  Almost everyone agrees that decorating/transforming a function at
> +  the end of its definition is suboptimal.  

One other point of agreement is that no one like having to write the
function name three times:
   def f():
       ...
   f = deco(f)



> +* Syntactic constraints.

There is an existing (though clumsy) syntax.   Most of the proposals are
less flexible but more elegant.  This trade-off has created much more
consternation than if there were no existing ways to apply decorations.



+* Overall unfamiliarity with the concept.  For people who have a
+  passing acquaintance with algebra (or even basic arithmetic) or have
+  used at least one other programming language, much of Python is
+  intuitive.  Very few people will have had any experience with the
+  decorator concept before encountering it in Python.  There's just no
+  strong preexisting meme that captures the concept.

My take on this one is that there are some existing memes from C# and
Java and that in the future they will be more widely known.

However, there are not good existing, thought-out concepts of what
exactly decorators should do in terms of preserving docstrings,
attributes, using parameters, etc.  Most have only a single application
in mind and the full implications (and possible applications) of a given
syntax are shrouded in the mists of the future.

Like metaclasses, everyone knew they were powerful when they were put
in, but no one knew how they would be used or whether they were
necessary.  In fact, two versions later, we still don't know those
answers.



Raymond