[Python-3000] iostack and Oh Oh (original) (raw)

Josiah Carlson jcarlson at uci.edu
Sat Dec 9 10:53:33 CET 2006

"Steven Bethard" <steven.bethard at gmail.com> wrote:

For the sake of DRY, I'd prefer to see::

class MyMapping: def mapping.getitem(self, key): ... def mapping.len(self): ...

I'd prefer to see...

class MyMapping:
    @implements(mapping)
    def __getitem__(self, key):
        ...
    
    @implements(mapping)
    def __len__(self):
        ...

Because then we don't need a new dotted name syntax proposal. The 3-argument type call would need to learn how to handle methods with @implements(interface) behavior defined, but other than that, I think it would work as-is.

P.S. Here's a 10 minute implementation of the above semantics that is almost backwards compatible with Python 2.3 (except for the decorator thing, which Python 2.3 has to do without).

_type = type

def make_interface(name, methods): return _type(name, (object,), dict([(nam, object()) for nam in methods]))

mapping = make_interface('mapping', mapping_methods) sequence = make_interface('sequence', sequence_methods) #...

_supports = {}

def supports(cls, interface): if interface in _supports: return cls in _supports[interface] return False

def implements(*interfaces): def foo(fcn): return implements_wrapper(fcn, interfaces) return foo

class implements_wrapper(object): slots = ['fcn', 'interfaces'] def init(self, fcn, interfaces): self.fcn = fcn self.interfaces = interfaces def call(self): return self.fcn, self.interfaces

def type(*args): if len(args) != 3: return _type(*args) name, bases, dct = args dct2 = {} for nam, obj in dct.items(): if isinstance(obj, implements_wrapper): f, i = obj() dct2[nam] = i dct[nam] = f cls = _type(name, bases, dct) for nam, i in dct2.iteritems(): for j in i: #default dict that produced sets would work well here _supports.setdefault(getattr(i, nam), {})[cls] = None return cls

builtins.type = type

More information about the Python-3000 mailing list