[Python-Dev] A usability argument for list-after-def (original) (raw)

Phillip J. Eby pje at telecommunity.com
Fri Aug 6 00:15:09 CEST 2004

At 11:52 PM 8/5/04 +0200, Gregory Lielens wrote:

> Of the options on the Wiki page ( at > http://www.python.org/moin/PythonDecorators ), this seems to > leave only > list-after-def, the previous community favorite and the first PEP 318 > syntax to have been implemented. > > Guido's principal argument against list-after-def, if I > recall correctly, > was that it is ugly when multiple or lengthy decorators are > involved. But, > "ugly" isn't an argument any more, so that shouldn't rule out > list-after-def. :)

On a cosmetic point of view, I also prefer the list-after-def syntax, first time I saw it it was the one than seemed the easiest (the "def f() as [decorator]" variant was event clearer, but the argument that as is only for renaming has mitigaed that somewhat ;-) ) "Cosmetic" does not sound like a very convincing argument, but I feel that this whole discussion is purely on a cosmetic level anyway, it is just a way to express more clearly something that is already possible...and as feedback as been asked for... ;-) But does it means that the list-after-def behaves like all lists, so that these are possible and equivalent? def foo() [decorator1, decorator2(bar)]: ... def foo() [ decorator1, decorator2(bar)]: ... mycomplexdecorator=[decorator1, decorator2(bar)] def foo() mycomplexdecorator : ...

The third example isn't allowed, but the first two are. Remember that part of the point is that the [] are being used to visually signal annotation. The third syntax loses this point.

Note that there is precedent for this kind of syntax restriction; a class' bases are a tuple, but that doesn't mean you can do this:

 yz = (Y,Z)

 class X yz:
     pass

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