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

Robert Brewer fumanchu at amor.org
Wed Mar 31 19:30:31 EST 2004

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:

  1. An argument which only applies if foo is inside the decorate block. I don't advocate that.
  2. Another.
  3. "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

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