On Mon, 16 Nov 2009 10:32:19 -0800, Steve Howell wrote:
> Actually, the __getitem__ workaround that I proposed earlier only works
> on subclasses of dict, not dict themselves. So given a pure dictionary
> object, it is impossible to hook into attribute lookups after
> instantiation in debugging/tracing code.
If you have written your application to avoid unnecessary isinstance and
type checks, i.e. to use duck-typing, then a technique you might find
useful is delegation.
class DebuggingDict(object):
def __init__(self, dict_to_wrap, hook=None):
self.__dict__['_d'] = dict_to_wrap
self.__dict__['getitem_hook'] = hook
def __getattr__(self, name):
return getattr(self._d, name)
def __setattr__(self, name, value):
setattr(self._d, name, value)
def __getitem__(self, key):
if self.getitem_hook is not None:
self.getitem_hook(self, key)
return self._d[key]
And in use:
>>> def hook(self, key):
... print "Looking for key", key
...
>>> d = DebuggingDict({1:'a', 2: 'b'}, hook)
>>> d[1]
Looking for key 1
'a'
>>> d[2]
Looking for key 2
'b'
--
Steven
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