<p>出于性能原因,Python总是在类(和父类)中查找magic方法,而不使用常规的属性查找机制。解决方法是在创建类时使用元类自动为magic方法添加代理;例如,我使用此技术避免了通过包装类的方法编写样板调用。</p>
<pre><code>class Wrapper(object):
"""Wrapper class that provides proxy access to an instance of some
internal instance."""
__wraps__ = None
__ignore__ = "class mro new init setattr getattr getattribute"
def __init__(self, obj):
if self.__wraps__ is None:
raise TypeError("base class Wrapper may not be instantiated")
elif isinstance(obj, self.__wraps__):
self._obj = obj
else:
raise ValueError("wrapped object must be of %s" % self.__wraps__)
# provide proxy access to regular attributes of wrapped object
def __getattr__(self, name):
return getattr(self._obj, name)
# create proxies for wrapped object's double-underscore attributes
class __metaclass__(type):
def __init__(cls, name, bases, dct):
def make_proxy(name):
def proxy(self, *args):
return getattr(self._obj, name)
return proxy
type.__init__(cls, name, bases, dct)
if cls.__wraps__:
ignore = set("__%s__" % n for n in cls.__ignore__.split())
for name in dir(cls.__wraps__):
if name.startswith("__"):
if name not in ignore and name not in dct:
setattr(cls, name, property(make_proxy(name)))
</code></pre>
<p>用法:</p>
<pre><code>class DictWrapper(Wrapper):
__wraps__ = dict
wrapped_dict = DictWrapper(dict(a=1, b=2, c=3))
# make sure it worked....
assert "b" in wrapped_dict # __contains__
assert wrapped_dict == dict(a=1, b=2, c=3) # __eq__
assert "'a': 1" in str(wrapped_dict) # __str__
assert wrapped_dict.__doc__.startswith("dict()") # __doc__
</code></pre>