Python Beginner - where comes <bound method ... of <... object at 0x0000000005EAAEB8>> from?

Question

I have a class

class ActivationResult(object):

    def __init__(self, successful : bool):
        self._successful = successful

    def getSuccessful(self) -> bool:
        return self._successful

And a test

def testSuccessfulFromCreate(self):

    target = ActivationResult(True)

    self.assertEquals(target._successful, True)
    self.assertEquals(target.getSuccessful, True)

The first assert is good, but the second one fails with AssertionError: <bound method ActivationResult.getSuccess[84 chars]EB8>> != True

The same thing happens, when I try to print it. Why?

Answer 1

You are getting the method, not calling it.
Try :

self.assertEquals(target.getSuccessful(), True)  # With parenthesss

It's OK the first time because you get the attribute _successful, which was correctly initialized with True.
But when you call target.getSuccessful it gives you the method object itself, where it seems like you want to actuall call that method.

---

Explanation

Here is an example of the same thing that happens when you print an object's method:

class Something(object):
    def somefunction(arg1, arg2=False):
        print("Hello SO!")
        return 42

We have a class, with a method.
Now if we print it, but not calling it :

s = Something()
print(s.somefunction)  # NO parentheses
>>> <bound method Something.somefunction of <__main__.Something object at 0x7fd27bb19110>>

We get the same output <bound method ... at 0x...> as in your issue. This is just how the method is represented when printed itself.

Now if we print it and actually call it:

s = Something()
print(s.somefunction())  # WITH parentheses
>>>Hello SO!
>>>42

The method is called (it prints Hello SO!), and its return is printed too (42)