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

Terry Reedy tjreedy at udel.edu
Sat Aug 7 07:05:55 CEST 2004

"Edward Loper" <edloper at gradient.cis.upenn.edu> wrote in message news:41145C05.1020501 at gradient.cis.upenn.edu...

The new "vertical bar" syntax was proposed recently, and has gotten almost unanimously positive feedback. In particular, of 17 responses to the syntax, only one has been negative (see table, below).

Add another +1. Verticle rules have been used before to tie several lines together, either as continuation lines or as sub-lines.

|classmethod |accepts(int, int) |returns(float) def foo(arg1, arg2): ...

def foo(arg1, arg2): |classmethod |accepts(int, int) |returns(float) ... (I prefer the second, but would be happy with either.)

Both logically and visually, I prefer the second also. By logically, I mean that it is more meaningful to me to read the decorators after reading that we are defining a function.

My main objection is that I like the idea that the header is definition time info and the body is run time code. I consider the doc string in the body to be a wart, not a precedence to by copied, but maybe I should think of the body as starting after the last | or the closing ''' :-).

The one negative comment was that "|" can look similar to "I" or "l", depending on the font; but it's only an issue for some fonts, and it should be largely mitigated by syntax-highlighting.

Is a space allowed after the prefic character, whatever it might be? With

def foo(): | classmethod | accepts(int,int) | returns(float)

the visual similarity to I doesn't matter much. Actual typos leading to test such as 'I returns' are guaranteed syntax errors, whereas a name such as Ireturns is not. The space even more clearly matches standard usage of a vertical rule and more clearly denotes the list as hanging off of 'def', so I would be tempted to require the space.

Terry J. Reedy

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