[Python-Dev] PEP318 metaclass approach
Sean Ross
sross at connect.carleton.ca
Sat Mar 27 15:10:06 EST 2004
Hi.
I've posted this code to python-list, but I thought I might post it
here as well. This is a metaclass approach to dealing with the issues
PEP318 is meant to address. It's a quick hack that allows you to put
the method decoration and annotation information before the method
definition. I just wanted to see if this could be done without changing
the language syntax. Looks like it's atleast a possibility, though this
only works with methods, and there are likly other issues I'm not aware
of. Anyway, here's the code:
import sys
def delayed_decorate(method, *decorators, **attributes):
"Decorate method during class instantation"
method.__dict__.update(attributes)
for decorator in decorators:
method = decorator(method)
return method
def decorate(funcname, *decorators, **attributes):
"Mark method for delayed decoration"
clsdict = sys._getframe(1).f_locals
clsdict.setdefault("decorated", {})[funcname] = \
(decorators, attributes)
class MetaDecorate(type):
"Enables delayed decoration and annotation of methods"
def __new__(klass, name, bases, _dict):
if "decorated" in _dict:
for m, (d, a) in _dict["decorated"].iteritems():
_dict[m] = delayed_decorate(_dict[m], *d, **a)
del _dict["decorated"]
return type.__new__(klass, name, bases, _dict)
class Decorated(object):
__metaclass__ = MetaDecorate
class C(Decorated):
a = "A"
decorate("f", classmethod, author="Sean Ross", version="0.9.2")
def f(klass):
return klass.a
decorate("g", staticmethod)
def g():
return "G"
print "C.f.author =", C.f.author
print "C.f.version =", C.f.version
print "C.f() =>", C.f()
print "C.g() =>", C.g()
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