foobar.py

def foo(func, *args, **kwargs):
    res = func(*args, **kwargs)
    return res["a key"]["in json"]["response"]

class A:
    def __init__(self, api):
        super().__init__()
        self.api = api

    def get_x(self):
        res = self.api.get_x()
        return res["a key"]["in json"]["response"]
    
    def get_y(self):
        res = self.api.get_y()
        return res["a key"]["in json"]["response"]
    
    @foo(self.api.get_x)
    def my_desired_get(self):
        pass