human
Solve the following python programming problem given the following code:
def _mock_assert_host_exists(self) : 
    "Sets it so that the host API always thinks that 'fake_host'
        exists.
        " 
    def fake_assert_host_exists(context, host_name, must_be_up = False) : 
        return 'fake_host' 
self.stubs.Set (self.host_api, '_assert_host_exists', <MASK>) 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: self
assistant
#Here is a proper replacement for <MASK>.
def fake_assert_host_exists(