At 07:32 AM 8/3/04 -0700, Guido van Rossum wrote:
> > In practical terms, all this means is that I'll just use the hacked
> > syntax until I no longer need to support Python 2.3.
>
>I don't understand why you prefer your hack over the established way
>to do decorators pre-2.4, which is
>
> def foo(): ...
> foo = staticmethod(foo)
For the same reason that PEP 318 was written in the first place: to improve
readability.
>This works across releases (including IronPython), doesn't require any
>magic, is documented, etc.
True; and most of my existing decorator-using code works this way, and I
don't plan on rushing out to change any of it any time soon.
> Isn't that much
>better than spending effort on hacks based on sys.settrace (which are
>surely going to produce bafflement from users who aren't familiar with
>that implementation hack)?
Well, up until recently, I thought the [] syntax was still a shoo-in and
that the settrace hack was just going to be a way to write
backwards-compatible code.
In the meantime, I've implemented a predicate-dispatch generic function
system using the settrace hack for PyProtocols 1.0, and don't want to have
to put off using it until 2.4. (FWIW, I still support 2.2.2, so "until
2.4" means maybe 1-2 years for me.) It looks like this:
[when("isinstance(x,Foo) and y>23")]
def do_something(x,y):
# code for when x is a Foo and y>23
[when("isinstance(x,Bar) and y<99")]
def do_something(x,y):
# code for when x is a Bar and y<99
Rendered without any decorator syntax, it would have to be something like:
def do_something_x_Foo_y_gt_23(x,y):
# code for when x is a Foo and y>23
do_something.add("isinstance(x,Foo) and y>23", do_something_x_Foo_y_gt_23)
def do_something_x_Bar_y_lt_99(x,y):
# code for when x is a Bar and y>99
do_something.add("isinstance(x,Bar) and y>23", do_something_x_Bar_y_lt_99)
...which is a significant loss in readability.
Now, it's true that this will just become '@when("whatever")' in 2.4, and
I'm *fine* with that, just disappointed that the syntax won't be forward
compatible.
Indeed, what I'd rather focus on is making sure that the *semantics* will
be forward compatible. Which I think they will be. What I'll probably do
is make 'when()' and other decorators return a callable that deactivates
the trace hack as a side effect of performing the decoration. That way,
[when()] and @when() can coexist in a code base during the migration period.
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