Hi,
I would like to create a Decorator metaclass, which automatically
turns a class which inherits from the "Decorator" type into a
decorator.
A decorator in this case, is simply a class which has all of its
decorator implementation inside a decorator() method. Every other
attribute access is being proxied to decorator().getParent().
Here's my attempt:
-------------------------------------------------------
from new import classobj
class DecoratorType(type):
def __new__(cls, name, bases, dct):
dct2 = {}
for key, val in dct.iteritems():
dct2[key] = val
# create a new class which will store all of the implementation
impl = classobj('%sImpl'%name,(),dct2)
# update the old class to implement this implementation
def __init__(self, *args, **dargs):
object.__setattr__(self, '__impl', impl(*args, **dargs))
def decorator(self):
return object.__getattribute__(self,'__impl')
def __getattribute__(self, attr):
if attr=="decorator":
return object.__getattribute__(self,'decorator')
return getattr(object.__getattribute__(self,
'decorator')
().getParent(), attr)
dct = {}
dct['__init__'] = __init__
dct['decorator'] = decorator
dct['__getattribute__'] = __getattribute__
return type.__new__(cls, name, bases, dct)
class Decorator(object):
__metaclass__ = DecoratorType
class HBar(Decorator):
def __init__(self, number):
Decorator.__init__(self)
self._number = number
def inc(self):
self._number += 1
def p(self):
print self._number
hbar = HBar(10)
for each in dir(hbar.decorator()):
print each
hbar.decorator().p()
hbar.decorator().inc()
hbar.decorator().p()
-------------------------------------------------------
Unfortunately this does not work. The newly defined __init__ method
inside __new__, does a call to impl(*args, **dargs). However, since
the HBar.__init__ calls the Decorator.__init__ method, but the
HBar.__init__ method no longer resides inside HBar, but rather inside
HBarImpl (which is no longer a subtype of Decorator), the compiler
complains that Decorator.__init__ is not being called with a Decorator
instance as its first argument (which is true).
I tried changing the definition of impl inside __new__ to have
Decorator as one of its bases, but then for some reason impl(*args,
**dargs) asks for 4 arguments (just like __new__) and I have no clue
as to why that happens.
Any help on this?
Regards,
Thomas K.
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