[Python-Dev] Re: Decorators: vertical bar syntax (original) (raw)

David Abrahams dave at boost-consulting.com
Mon Aug 9 15:34:58 CEST 2004

Bill Janssen <janssen at parc.com> writes:

In the discussion on decorators months ago, solutions involving special syntax inside the block were ruled out early on. Basically, you shouldn't have to peek inside the block to find out important external properties of the function. Guido, could you expand on this principle a bit? Just stated as it is, it sounds as pointless (to my untutored mind, at least :-), as the arguments about "@ is ugly, so it shouldn't be used". After all, isn't "what the function does" an important external property of the function, and don't you have to peek inside the block to determine that? For instance, how do you know whether a function is a generator unless you look for yield statements inside it?

I'm not Guido (obviously), but:

You look at the documentation. The fact that Python doesn't divorce interface declarations from implementation is convenient for authors, but in some ways a trap for readers/maintainers (this is not a design criticism -- it was probably the right design choice). I often have to look inside Python functions to understand them, and find that their authors expect me to do so. I think a style that cleanly delimits interface and implementation as much as possible should be encouraged. The fact that docstrings sit inside the function block make that harder to achieve; that's why I'm glad to hear that prefix decorators are being considered for docstrings.

That said, I'm not sure that "immediately following the opening colon" is such a bad place for interface-y things. It's nice that you can find the whole function's declaration by looking forward from "def ..." today [except for the decorators, of course ;-(].

-- Dave Abrahams Boost Consulting http://www.boost-consulting.com

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