[Python-Dev] PEP 318: Decorators last before colon

[Shane Hathaway]

On 03/30/04 16:21, Guido van Rossum wrote:
>>Another possibility that has been suggested is
>>
>>[decorator] 
>>def func(arg, arg):
> 
> And one that I currently favor.  I'm out of bandwidth to participate
> on a msg-by-msg basis, but perhaps folks can see if they can come to
> terms with this solution?

+1.  We had a short email exchange about this a while ago.  I'm glad 
it's back on the table.  It's elegant, and the decorations people are 
already using will become more apparent than they are today.

This is important to me because decorators need to be very visible.  One 
class I frequently use (SimpleVocabulary in Zope 3) drove me crazy at 
first until I understood the pattern the author had used.  The 
constructor takes two strange arguments, and for quite a while I 
couldn't figure out just what it wanted.  Finally, I noticed that the 
class has several classmethods, and they all call the constructor.  The 
author intended users to call the classmethods, not the constructor, but 
it was hard to notice any classmethods since the word "classmethod" was 
buried below the function body.  Using "cls" as a first argument didn't 
help, since I've practically trained my eyes to ignore the first argument.

Zope has experimented with several ways of decorating methods with 
security declarations.  Here are some of the variations attempted so far:


class Foo:
     __ac_permissions__ = (('bar', 'View management screens'),)
     def bar(self):
         pass
InitializeClass(Foo)  # Finds __ac_permissions__ and changes methods

class Foo:
     bar__roles__ = PermissionRole('View management screens')
     def bar(self):
         pass

class Foo:
     security = ClassSecurityInfo()
     security.declareProtected('View management screens', 'bar')
     def bar(self):
         pass
InitializeClass(Foo)  # Finds a ClassSecurityInfo and calls it


These are all bad enough that Zope 3 has chosen to make no such 
declarations at all in Python code, putting them in XML instead.  That 
may be the right choice for Zope 3, but surely other Python developers 
are running into similar needs on their own projects.  They shouldn't 
have to go through this pain.  They should be able to start with 
something clean like this:


class Foo:
     [protected('View management screens')]
     def bar(self):
         pass


Shane