human
Solve the following python programming problem given the following code:
@ gen_test 
def test_stack_context(self) : 
    loop = self.io_loop 
    history = [] 
    cx = self.motor_client (max_pool_size = 1) 
    (yield cx.motor_test.test_collection.find_one ()) 
    pool = cx._get_primary_pool () 
    self.assertEqual (1, len (pool.sockets)) 
    sock_info = pool.get_socket () 
    main_gr = greenlet.getcurrent () 
    def catch_get_sock_exc(exc_type, exc_value, exc_traceback) : 
        history.extend (['get_sock_exc', exc_value]) 
        return True 
def catch_return_sock_exc(exc_type, exc_value, exc_traceback) : 
        history.extend (['return_sock_exc', exc_value]) 
        return True 
def get_socket() : 
        pool.get_socket () 
        loop.add_callback (raise_callback) 
my_assert = AssertionError ('foo') 
    def raise_callback() : 
        history.append ('raise') 
        raise my_assert 
def return_socket() : 
        with stack_context.ExceptionStackContext (catch_return_sock_exc) : 
            pool.maybe_return_socket (sock_info) 
main_gr.switch () 
with stack_context.ExceptionStackContext (<MASK>) : 
        loop.add_callback (greenlet.greenlet (get_socket).switch) 
greenlet.greenlet (return_socket).switch () 
    (yield self.pause (0.1)) 
    self.assertEqual (['raise', 'get_sock_exc', my_assert], history) 
    cx.close () 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: my_assert, self, sock_info, get_socket, main_gr, history, return_socket, catch_return_sock_exc, pool, raise_callback, loop, cx
assistant
#Here is a proper replacement for <MASK>.
def catch_get_sock_exc(