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

[Robert Brewer]

Ka-Ping Yee wrote:
> This discussion is turning in a direction that alarms me.
> 
> Putting the [decorator] on a separate line before the function
> changes the stakes entirely.  It sets aside real functional issues
> in favour of aesthetics.  Being enamoured with the way this syntax
> *looks* does not justify functionally *breaking* other things in
> the implementation to achieve it.
> 
> Consider the arguments in favour:
> 
>     1.  Decorators appear first.
>     2.  Function signature and body remain an intact unit.
>     3.  Decorators can be placed close to the function name.
> 
> These are all aesthetic arguments: they boil down to "the appearance
> is more logical".  Similar arguments have been made about the other
> proposals.
> 
> Consider the arguments against:
> 
>     1.  Previously valid code has new semantics.
>     2.  Parse tree doesn't reflect semantics.
>     3.  Inconsistent interactive and non-interactive behaviour. [*]
>     4.  Decorators can be arbitrarily far away from the function name.

Agreed, although I won't use such alarmist phrases. ;)

Notice that the form:

decorate:
    dec1
    dec2
def foo(arg1, arg2, ...):
    pass

gives all of the benefits you mentioned without incurring any of the
"arguments against", except possibly #4. The PEP itself gives the
"arguments against" this form as:

1. "The function definition is not nested within the using: block making
it impossible to tell which objects following the block will be
decorated"

Somewhat of an oblique argument, to which the simple answer is: there
must be a def right after it, in exactly the same manner that a try:
must be followed by an except: or finally:

2. An argument which only applies if foo is inside the decorate block. I
don't advocate that.
3. Another.
4. "Finally, it would require the introduction of a new keyword."

Yup. Not a bad thing for such a powerful tool, IMO.


Robert Brewer
MIS
Amor Ministries
fumanchu at amor.org