with the new class decorators of py3k, new use cases emerge.
for example, now it is easy to have real mixin classes or even
mixin modules, a la ruby.
unlike inheritance, this mixin mechanism simply merges the
namespace of the class or module into the namespace of the
decorated class. it does not affect class hierarchies/MRO,
and provides finer granularity as to what methods are merged,
i.e., you explicit mark which methods should be merged.
def mixinmethod(func):
"""marks a method as a mixin method"""
func.is_mixin = True
return func
def get_unbound(obj, name):
if name in obj.__dict__:
return obj.__dict__[name]
else:
for b in obj.mro():
if name in b.__dict__:
return b.__dict__[name]
def mixin(obj, override = False):
"""a class decorator that merges the attributes of 'obj' into the class"""
def wrapper(cls):
for name in dir(obj):
attr = get_unbound(obj, name)
if getattr(attr, "is_mixin", False):
if override or not hasattr(cls, name):
setattr(cls, name, attr)
return cls
return wrapper
Example
==================
class DictMixin:
@mixinmethod
def __iter__(self):
for k in self.keys():
yield k
@mixinmethod
def has_key(self, key):
try:
value = self[key]
except KeyError:
return False
return True
@mixinmethod
def clear(self):
for key in self.keys():
del self[key]
...
@mixin(DictMixin)
class MyDict:
def keys(self):
return range(10)
md = MyDict()
for k in md:
print k
==================================
does it seem useful? should it be included in some stdlib?
or at least mentioned as a use case for class decorators in PEP 3129?
(not intended for 3.0a1)
-tomer
_______________________________________________
Python-3000 mailing list
Python-3000@python.org
http://mail.python.org/mailman/listinfo/python-3000
Unsubscribe:
http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
