[Python-Dev] PEP 318: Decorators last before colon (original) (raw)

Guido van Rossum guido at python.org
Tue Mar 30 17:58:41 EST 2004

The most obvious issues I see with this is are that: - grepping for "def func" won't show any sign that its decorated, and

Seems rather minor -- there's only so much you can cram on a single line.

- it looks like normal syntax, so it looks like expressions should work, e.g.

[decorator1] + [decorator2] def func(arg, arg): or even: getstddecorators() # Returns a list def func(arg, arg): I'm pretty sure this isn't the intention, though. I can imagine some posts to comp.lang.python asking how to do the above...

The same syntactic restrictions apply to docstrings (you can't have an expression of type string in the docstring position, it has to be a literal). Nobody's confused by that one.

Neither of these are fatal flaws, but I think I still prefer:

def func(args) [decorator]:

Which hides 'classmethod' behind the more voluminous stuff, and that's my main gripe.

My main reasoning is as follows:

  1. If we do decorators at all, decorators should be allowed to be arbitrary expressions.

  2. Since we allow arbitrary expressions, decorators provide a much better way to set function attributes than the current way.

  3. This will be attractive (better than putting special mark-up in docstrings), so there will be lots of voluminous decorators.

  4. Then the "important" decorators like classmethod will be hidden at the end of the list of decorators.

The [...] prefix proposal addresses this by putting the end of the decorator list closest to the def keyword. This doesn't look so bad:

[funcattr(spark="<spark syntax here>",
          deprecated=True,
          overrides=True),
 classmethod]
def foo(cls, arg1, arg2):
    pass

--Guido van Rossum (home page: http://www.python.org/~guido/)

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