What does "if self is not None" mean in a method?

class omnimethod(object):
    def __init__(self, func):
        self.func = func

    def __get__(self, instance, owner):
        return functools.partial(self.func, instance)

class Geocoder(object):
        def __init__(self, api_key=None, client_id=None, private_key=None):
            # omitted
            pass

        @omnimethod
        def geocode(
            self,
            address,
            sensor='false',
            bounds='',
            region='',
            language='',
            components=''):
                if self is not None:  # <-- here
                    return GeocoderResult(self.get_data(params=params))
                else:
                    return GeocoderResult(Geocoder.get_data(params=params))

Exactly in this case.

I didn't understand. What does this "if self is not None" code snippet mean? What is its place in the case? This self is parameter, in the function parameter. But alone.

Solution

omnimethod looks to be a decorator intended for a function it's applied to to be invoked either as an instance or a class method.

Let's call the original function original and the result of applying the decorator, which becomes the geocode attribute of class Geocoder, decorated.

Consider two calls:

Geocoder.geocode("some address")  # 1
geocoder = Geocoder()
geocoder.geocode("some address")  # 2

According to the descriptor protocol:

The call (1) will resolve to:

decorated.__get__(None, Geocoder)("some address"), which returns the original function partially applied to None:
functools.partial(original, None)("some address"), which, according to implementation of partial, is the same as:
original(None, "some address")

The call (2) will resolve to:

decorated.__get__(geocoder, Geocoder)("some address") (where geocoder is an instance of Geocoder)
functools.partial(original, geocoder)("some address")
original(geocoder, "some address")

Thus, self will be None inside the original function if it is invoked as a class method, necessitating the check.