Python - how can I dynamically remove a method from a class -- i.e. opposite of setattr

Question

I don't know if I have a good design here, but I have a class that is derived from unittest.TestCase and the way I have it set up, my code will dynamically inject a bunch of test_* methods into the class before invoking unittest to run through it. I use setattr for this. This has been working well, but now I have a situation in which I want to remove the methods I previously injected and inject a new set of methods. How can I remove all the methods in a class whose names match the pattern test_*?

Answer 1

It's called delattr and is documented here.

Answer 2

>>> class Foo:
    def func(self):
        pass
...     
>>> dir(Foo)
['__doc__', '__module__', 'func']
>>> del Foo.func
>>> dir(Foo)
['__doc__', '__module__']

Answer 3

delattr() is what you want. Loop through vars() of the class and test for attribute names starting with "test_". E.g.,

@classmethod
def remove_test_methods(cls):
    for name in list(vars(cls)):
        if name.startswith("test_") and callable(getattr(cls, name)):
            delattr(cls, name)

I'd advise against using dir(), as this will show you names from your parent classes as well, so not all the names you get from dir() may defined on the class you're targeting.

Answer 4

As an addition to the previous answers: If the method to be deleted is re-implemented, you'd have to delete the subclass and parent class methods, both:

class A:
    def method(self): 
        print("TestA")

class B(A):
    def method(self):
        A.method(self)
        print("TestB")

instance = B()
instance.method() # will call B.method()
del B.method
instance.method() # will now call A.method()
del A.method
instance.method() # will now raise AttributeError

(Or use delattr of @BrenBarn's answer)