Greg Ewing wrote:
> Kendall Clark wrote:
>>One thing I'd really like to see in Python 3000 is support for first-
>>class symbols,
>>
>> def web_dispatch("/bank-account", :GET, retrieve_account): pass
>
>
> class SymGen:
>
> def __getattr__(self, name):
> return intern(name)
>
> sym = SymGen()
>
> web_dispatch("/bank-account", sym.GET, retrieve_account)
The advantage of an enumerator would be more if it was namespace. E.g.:
class Sym:
def __init__(self, parent, name):
self.parent = parent
self.name = name
def __repr__(self):
return '<Symbol %s.%s>' % (self.parent, self.name)
class SymGen:
def __init__(self, name=None):
if name is None:
name = self.__class__.__name__
self.name = name
def __getattr__(self, attr):
sym = Sym(self.name, attr)
setattr(self, attr, sym)
return sym
Considering the namespace, the difference between enumerations and
symbols becomes a little more clear (though certainly symbols are used
for enumerations in languages that have symbols). You can't use an
enumeration from a namespace for a method name, for example.
Steven's proposal in another thread for a 'make' statement
(http://ucsu.colorado.edu/~bethard/py/pep_make_statement.html) would
alleviate some of the motivation for symbols. E.g., currently:
class MyTable(MyORM):
mycol = Column('mycol', type=Int)
That is, barring metaclass tricks that require cooperation with Column,
you have to pass the column's name into it. So 'mycol' is really a
Python identifier without a namespace, represented as a string. This is
what they seem to do a lot of in Ruby. For instance (assuming class
decorators were adopted) this is how they might set up a property:
class Foo:
@class attr('bar')
Which would add a 'bar' attribute (which doesn't really make sense in
Python since we have public instance variables, and Ruby only has private).
But the make syntax offers an alternative:
class MyTable(MyORM):
make Column mycol:
type = Int
Now there's no strings, the identifier isn't repeated, and its clear
that "mycol" is an identifier, not a string or a mere variable binding.
--
Ian Bicking / [EMAIL PROTECTED] / http://blog.ianbicking.org
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