[Python-Dev] Early PEP draft (For Python 3000?)
jcarlson at uci.edu
Thu Oct 20 18:48:43 CEST 2005
Jim Jewett <jimjjewett at gmail.com> wrote:
> I'll try to be more explicit; if Josiah and I are talking past each
> other, than the explanation was clearly not yet mature.
> (In http://mail.python.org/pipermail/python-dev/2005-October/057251.html)
> Eyal Lotem suggested:
> > Name: Attribute access for all namespaces ...
> > global x ; x = 1
> > Replaced by:
> > module.x = 1
> I responded:
> > Attribute access as an option would be nice, but might be slower.
> > Also note that one common use for a __dict__ is that you don't
> > know what keys are available; meeting this use case with
> > attribute access would require some extra machinery, such as
> > an iterator over attributes.
> Josiah Carlson responded
> > This particular use case is easily handled. Put the following
> > once at the top of the module...
> > module = __import__(__name__)
> > Then one can access (though perhaps not quickly) the module-level
> > variables for that module. To access attributes, it is a quick scan
> > through module.__dict__, dir(), or vars().
> My understanding of the request was that all namespaces --
> including those returned by globals() and locals() -- should
> be used with attribute access *instead* of __dict__ access.
Yeah, I missed the transition from arbitrary stack frame access to
strictly global and local scope attribute access.
> module.x is certainly nicer than module.__dict__['x']
> Even with globals() and locals(), I usually *wish* I could
> use attribute access, to avoid creating a string when what
> I really want is a name.
> The catch is that sometimes I don't know the names in
> advance, and have to iterate over the dict -- as you
> suggested. That works fine today; my question is what
> to do instead if __dict__ is unavailable.
> Note that vars(obj) itself conceptually returns a NameSpace
> rather than a dict, so that isn't the answer.
vars([object]) -> dictionary
Without arguments, equivalent to locals().
With an argument, equivalent to object.__dict__.
When an object lacks a dictionary, dir() works just fine.
Help on built-in function dir:
dir([object]) -> list of strings
Return an alphabetized list of names comprising (some of) the attributes
of the given object, and of attributes reachable from it:
No argument: the names in the current scope.
Module object: the module attributes.
Type or class object: its attributes, and recursively the attributes of
Otherwise: its attributes, its class's attributes, and recursively the
attributes of its class's base classes.
> My inclination is to add an __iterattr__ that returns
> (attribute name, attribute value) pairs, and to make this the
> default iterator for NameSpace objects.
for i in dir(obj):
yield i, getattr(obj, i)
> Whether the good of
> (1) not needing to mess with __dict__, and
> (2) not needing to pretend that strings are names
> is enough to justify an extra magic method ... I'm not as sure.
I don't know, but leaning towards no; dir() works pretty well. Yeah, you
have to use getattr(), but there are worse things.
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