classmethod lambda Python

Question

I'm having a hard time understanding this piece of code. I understand that we are using some mock instead of the API endpoint to save time on the tests.

What I don't understand is the classmethod(lambda cls: self.preapproval) structure. What is the point of using a lambda cls if inside the code I don't use at all the cls.

I hope I'm clear enough, I'd be very happy if someone could shed some light on this one..

Thanks a lot.

@patch("paypaladaptive.api.endpoints.UrlRequest",
       MockUrlRequestPreapproval)
def test_preapproval(self):
    # I don't understand this code, it is very confusing. Why do I need to use a lambda structure if in the code itself I don't use cls (self.preapproval)
    MockUrlRequestPreapproval.preapproval = (
        classmethod(lambda cls: self.preapproval))
    self.assertTrue(self.preapproval.process())
    self.preapproval = Preapproval.objects.get(pk=self.preapproval.pk)
    self.assertNotEqual(self.preapproval.preapproval_key, "")
    self.assertEqual(self.preapproval.status, "created")

Answer 1

classmethod's first argument needs to be a function that takes one argument or more. Calling any of this will cause an error:

classmethod(self.preapproval) # Not a function
classmethod(lambda: self.preapproval) # Needs one argument

This works, but it's too verbose:

def get_preapproval(cls):
    return self.preapproval

classmethod(get_preapproval)

That's why that code uses lambda.

Probably it can be improved a little bit:

classmethod(lambda _: self.preapproval)

This makes it obvious that the argument is not needed.