Python equivalent of Ruby's 'method_missing'

Question

What is Python's equivalent of Ruby's method_missing method? I tried using __getattr__ but this hook applies to fields too. I only want to intercept the method invocations. What is the Python way to do it?

Answer 1

There is no difference in Python between properties and methods. A method is just a property, whose type is just instancemethod, that happens to be callable (supports __call__).

If you want to implement this, your __getattr__ method should return a function (a lambda or a regular def, whatever suite your needs) and maybe check something after the call.

Answer 2

Python doesn't distinguish between methods and attributes (a.k.a. "instance variables") the way Ruby does. Methods and other object attributes are looked up in exactly the same way in Python -- not even Python knows the difference at the look-up stage. Until the attribute is found, it's just a string.

So if you're asking for a way to ensure that __getattr__ is only called for methods, I'm afraid you probably won't find an elegant solution. But it's easy enough to simply return a function (or even a brand-new dynamically bound method) from __getattr__.