[Python-Dev] Re: def fn (args) [dec,dec]: (original) (raw)

Guido van Rossum guido at python.org
Fri Aug 6 16:45:51 CEST 2004

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[Anthony]

I'm having trouble finding a single piece from you where you outline the problems you have with the [decorators] after args, before :. Could you possibly post a message to python-dev stating your problems with it? It's the major one I've been unable to find your objections to.

And nobody else has expressed their objections to it either? :-)

Just look at it when either the list of decorators or the argument list doesn't fit on one line:

class C(object):

def longMethodNameForEffect(longArgumentOne=None,
                            longArgumentTwo=42) [
    staticmethod,
    funcattrs(grammar="'@' dotted_name [ '(' [arglist] ')' ]",
              status="experimental", author="BDFL")
    ]:
    """This method blah, blah.

    It supports the following arguments:
- longArgumentOne -- a string giving ...
    - longArgumentTwo -- a number giving ...

blah, blah.

"""
    raise NotYetImplemented

That's a total jumble of stuff ending with a smiley. (True story: I left out the colon when typing up this example and only noticed in proofing.)

Problems with this form:

• it hides crucial information (e.g. that it is a static method) after the signature, where it is easily missed

• it's easy to miss the transition between a long argument list and a long decorator list

• it's cumbersome to cut and paste a decorator list for reuse, because it starts and ends in the middle of a line

Given that the whole point of adding decorator syntax is to move the decorator from the end ("foo = staticmethod(foo)" after a 100-line body) to the front, where it is more in-your-face, it should IMO be moved all the way to the front.

(If I could design a language from scratch, I might want to move docstrings to before the 'def' as well; I've come to appreciate this in Java code. Fredrik Lundh's PythonDoc also uses comments prefixing the method definition; he also uses @ so he should be happy with this syntax, as he seemed to be when I mentioned it to him at EuroPython.)

--Guido van Rossum (home page: http://www.python.org/~guido/)

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