[Python-Dev] @-after-def-before-colon (was Re: def ... decorate) (original) (raw)

Phillip J. Eby pje at telecommunity.com
Fri Aug 13 20:26:14 CEST 2004

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At 07:52 PM 8/13/04 +0200, Werner Schiendl wrote:

was the following suggested already? (don't think so):

def pstatementexpr(self, p): staticmethod grammarrule('statement : expression') version("Added in 2.4") deprecatedmethod type(None) body: """docstring here""" print p[1]

hmmmm.... that's really not much different from:

def p_statement_expr(self, p) [
    staticmethod,
    grammarrule('statement : expression'),
    version("Added in 2.4"),
    returns(None)
]:
    """Docstring"""
    body

is it?

But then, how about this:

def p_statement_expr(self, p)
    @staticmethod
    @grammarrule('statement : expression')
    @version("Added in 2.4")
    @returns(None)
as:
    """Docstring"""
    body

The decorators are much more visible with the @ signs. Also, we could possibly allow the docstring to appear in the def statement, rather than in the body, e.g.:

def p_statement_expr(self, p)
    @staticmethod
    @grammarrule('statement : expression')
    @version("Added in 2.4")
    @returns(None)
    """Docstring"""
as:
    body

Some advantages:

• Tools that just only look at 'def funcname(signature)' still work

• Tools that only look for '@something' at the start of the line will work (e.g. I believe this means IPython will still work, dunno about Leo)

• Decorators are much more visible than in the list-after-def forms, but are still visibly part of the function definition

• You know the name/signature of the thing being defined before wading through decorators

Disadvantages:

• line continuation isn't standard; there ought to be brackets or parentheses, otherwise tokenizer will say there's an INDENT, and it's not standard to have an INDENT without a colon.

• How would we define the syntax? Should it be something like this:

  classdef: 'class' NAME ['(' testlist ')'] [decorations] ':' suite funcdef: 'def' NAME parameters [decorations] ':' suite

  decorations: NEWLINE INDENT decorator* [docstring NEWLINE] DEDENT 'as' decorator: '@' test NEWLINE

In other words, should indent and one-decorator-per-line be enforced?

• Guido has argued that list-after-def is bad in the case of a long argument list, because of poor visibility. Does this approach fix that?

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