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

Fernando Perez fperez528 at yahoo.com
Mon Aug 9 19:50:19 CEST 2004

Guido van Rossum wrote:

[Guido]

> 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. [Bill Janssen] Guido, could you expand on this principle a bit? Just stated as it

It's probably untenable as a formal principle. :-)

Nevertheless I don't like to put decorators in the method body. I think it has something to do with the fact that normally one thinks of the body contents as relevalt to "call-time" while decorators happen at "definition-time".

I realize what your current position on this topic is, but I'd like to encourage you to at least reconsider it for a moment. In python we've come to consider, for better or worse, the section up to the end of the docstring, as a kind of 'header' or 'interface' zone for functions. I know you dislike the docstrings as an example of this, but in fact I don't view it as such a bad thing: the def indents and clearly separates the function, and for a while you have 'interface' information: function name, argument list, docstring, and perhaps now decorators. This actually feels very clean to me, and seems to nicely fit the mental model of how python works.

Elsewhere in this thread: http://mail.python.org/pipermail/python-dev/2004-August/047326.html and below, I tried to make a reasoned argument in defense of this. I won't repeat all that here.

I further worry what will happen to tools like inspect.getsource() with decorators outside the def:

@foo @bar def baz(x,y): ....

if I try to get the source for baz, will I see foo/bar? For introspection tools, this can lead to pretty misleading results. But perhaps this is easy to solve or has even already been taken care of. I imagine if @foo/@bar were inside the def, this wouldn't be an issue.

Best,

f

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