On Nov 7, 11:03 pm, "[email protected]"
<[email protected]> wrote:
...
> These quick fixes aren't ideal as they rely on too much knowledge by the
> subclass, but they shed light on what's going on. I'll leave a better fix
> as an exercise for the reader ... ;)
The exercise for the reader is that the problem is that the Proxy
class needed to have the same __class__ as the object it's wrapping.
The "obvious" way to do this though results in infinite mutual
recursion.
ie you can't do this:
def mydec(klass):
class Proxy(object):
__metaclass__ = AttributeProxying
...
return Proxy
class AttributeProxying(type):
def __new__(meta, name, bases, Dict):
... snip...
return mydec(klass, name, bases, newdict)
class Proxied(object):
__metaclass__ = AttributeProxying
...
class SafeStore(Proxied):
pass
Since that results in mutual recursion and blows the stack.
What you can do though is this:
def mydec(klass, name, bases, newdict):
def __init__(self, *args,**argd):
....
def __getattribute__(self, key):
....
# Build a dict for the proxy class containing __module__
# (matching klass), __init__ and __getattribute__
# We add in one attribute:
proxy_dict["__norecurse__"] = True
# Then make the Proxy class
Proxy = klass.__class__(name +"_Proxy", bases, proxy_dict)
return Proxy
class AttributeProxying(type):
def __new__(meta, name, bases, Dict):
... snip...
# We then modify things such that if we detect we're
# being called by mydec we only return the klass
if newdict.get("__norecurse__", False):
return klass
# Otherwise we call the class decorator, and return that
return mydec(klass, name, bases, newdict)
class Proxied(object):
__metaclass__ = AttributeProxying
...
class SafeStore(Proxied):
pass
And then that does work as expected, with inheritance of the metaclass
re-enabled.
Pastebin of working minimal example:
* http://pastebin.com/04RcPwPT
Pastebin of the output of that minimal working example:
* http://pastebin.com/TXvGLES3
Thanks for the feedback earlier in the week, much appreciated :-)
Michael.
--
To post: [email protected]
To unsubscribe: [email protected]
Feeds: http://groups.google.com/group/python-north-west/feeds
More options: http://groups.google.com/group/python-north-west
