[Python-Dev] New syntax for 'dynamic' attribute access

[Guido van Rossum]

Oh, now I am definitely in favor of .[]! I read it in gmail in FireFox
which uses a small variable-pitch font whose dot is a single pixel.
The .() example was hard to find; the .[] jumped out immediately.
(When do you ever see self[anything]?)

On 2/12/07, Brett Cannon <brett at python.org> wrote:
> On 2/12/07, Guido van Rossum <guido at python.org> wrote:
> > FWIW, I'm strongly -1 on the "->" notation. As a C programmer it's got
> > too many neurons committed to it.
> >
> > I recommend that you do some experiments with the readability of the
> > .[...] notation, e.g. write a program that randomly generates x.[foo]
> > and x[foo], and see how fast you can spot the difference. I bet that
> > you won't have any trouble.
> >
>
> OK, so real-world examples.  First, ``foo.(name)``, from urllib.py::
>
>         name = 'open_' + urltype
>         self.type = urltype
>         name = name.replace('-', '_')
>         if not hasattr(self, name):
>             if proxy:
>                 return self.open_unknown_proxy(proxy, fullurl, data)
>             else:
>                 return self.open_unknown(fullurl, data)
>         try:
>             if data is None:
>                 return self.(name)(url)
>             else:
>                 return self.(name)(url, data)
>         except socket.error, msg:
>             raise IOError, ('socket error', msg), sys.exc_info()[2]
>
> and also::
>
>         name = 'http_error_%d' % errcode
>         if hasattr(self, name):
>             method = self.(name)
>             if data is None:
>                 result = method(url, fp, errcode, errmsg, headers)
>             else:
>                 result = method(url, fp, errcode, errmsg, headers, data)
>             if result: return result
>         return self.http_error_default(url, fp, errcode, errmsg, headers)
>
>
> And here is urllib2.py for ``.[]`` (used different files so you
> wouldn't just remember where the change was)::
>
>         if attr[:12] == '_Request__r_':
>             name = attr[12:]
>             if hasattr(Request, 'get_' + name):
>                 self.['get_' + name]()
>                 return self.[attr]
>         raise AttributeError, attr
>
> and::
>
>         handlers = chain.get(kind, ())
>         for handler in handlers:
>             func = handler.[meth_name]
>             result = func(*args)
>             if result is not None:
>                 return result
>
>
>
> Neither version jumps out at me strongly, although between the two the
> ``.[]`` version shows up the best.  But that might also be because of
> the lower noise when used in a call.
>
> -Brett
>


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