Question

I am trying to prevent an instance from throwing an exception if a method that does not exist for the instance is called. I have tried the following:

class myClass(object):
    def __init__(self):
        pass
    def __getattr__(self,name):
        print "Warning - method {0} does not exist for this instance".format(name)

o = myClass()
var = o.someNonExistantFunction()

The problem is that I get the following error:

TypeError: 'NoneType' object is not callable

The two things I want to make sure of doing is:

1. Return None as my code can deal with variables being set to None
2. Perform a function (printing a warning message)

What is the cleanest way to do this?

Answer 1

return a function that does nothing?

Couple of things: first you might want to use __getattr__ rather than __getattribute__.
__getattr__ gets called when the runtime doesn’t find anything by that name in the hierarchy, __getattribute__ gets called every time.

class Test(object):
    def __getattr__(self,key):
        def placeholder(*args, **kwargs):
            print "Warning - method '%s' does not exist for this instance"%key
        return placeholder