On Wednesday 14 December 2016 17:11, Veek M wrote: > I know that with user classes one can define getattr, setattr to handle > dictionary lookup. Is there a way to hook into the native dict() type > and see in real time what's being queried.
Not easily, and maybe not at all. There are two obvious ways to do this: (1) monkey-patch the object's __dict__, and the class __dict__. Unfortunately, Python doesn't support monkey-patching built-ins. https://en.wikipedia.org/wiki/Monkey_patch Or perhaps I should say, *fortunately* Python doesn't support it. http://www.virtuouscode.com/2008/02/23/why-monkeypatching-is-destroying-ruby/ (2) Alternatively, you could make a dict subclass, and replace the class and instance __dict__ with your own. Unfortunately, you cannot replace the __dict__ of a class: py> class X: # the class you want to hook into ... pass ... py> class MyDict(dict): # my custom dict ... def __getitem__(self, key): ... print(key) ... return super().__getitem__(key) ... py> d = MyDict() py> d.update(X.__dict__) py> X.__dict__ = d Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: attribute '__dict__' of 'type' objects is not writable You can replace the instance dict, but Python won't call your __getitem__ method: py> instance = X() py> instance.__dict__ = MyDict() py> instance.a = 999 py> instance.a 999 So the short answer is, No. You might be able to create a completely new metaclass that supports this, but it would be a lot of work, and I'm not even sure that it would be successful. > I wanted to check if when one does: > > x.sin() > > if the x.__dict__ was queried or if the Foo.__dict__ was queried.. The easiest way to do that is something like this: py> class Test: ... def sin(self): ... return 999 ... py> x = Test() py> x.sin <bound method Test.sin of <__main__.Test object at 0xb6fc3a4c>> py> x.sin() 999 py> x.sin = "surprise!" py> x.sin 'surprise!' So now you know: an instance attribute will shadow the class attribute. (Actually, that's not *completely* true. It depends on whether x.sin is a descriptor or not, and if so, what kind of descriptor.) -- Steven "Ever since I learned about confirmation bias, I've been seeing it everywhere." - Jon Ronson -- https://mail.python.org/mailman/listinfo/python-list
