human
Solve the following python programming problem given the following code:
def __init__(self, init_only = None, v3mode = False) : 
    def _check_load_extension(ext) : 
        if (((self.init_only is None) or (ext.obj.alias in self.init_only)) and isinstance (ext.obj, extensions.V21APIExtensionBase)) : 
            if ((not CONF.osapi_v21.extensions_whitelist) or (ext.obj.alias in CONF.osapi_v21.extensions_whitelist)) : 
                blacklist = CONF.osapi_v21.extensions_blacklist 
                if (ext.obj.alias not in blacklist) : 
                    return self._register_extension (ext) 
return False 
if (CONF.osapi_v21.extensions_blacklist or CONF.osapi_v21.extensions_whitelist) : 
        LOG.warning (_LW ('In the M release you must run all of the API. The concept of API extensions will be removed from the codebase to ensure there is a single Compute API.')) 
self.init_only = init_only 
    LOG.debug ('v21 API Extension Blacklist: %s', CONF.osapi_v21.extensions_blacklist) 
    LOG.debug ('v21 API Extension Whitelist: %s', CONF.osapi_v21.extensions_whitelist) 
    in_blacklist_and_whitelist = set (CONF.osapi_v21.extensions_whitelist).intersection (CONF.osapi_v21.extensions_blacklist) 
    if (len (in_blacklist_and_whitelist) != 0) : 
        LOG.warning (_LW ('Extensions in both blacklist and whitelist: %s'), list (in_blacklist_and_whitelist)) 
self.api_extension_manager = stevedore.enabled.EnabledExtensionManager (namespace = self.api_extension_namespace (), check_func = _check_load_extension, invoke_on_load = True, invoke_kwds = { 
        'extension_info' : self.loaded_extension_info, 
}) 
    if v3mode : 
        mapper = PlainMapper () 
else : 
        mapper = ProjectMapper () 
self.resources = { 
        
} 
    if list (self.api_extension_manager) : 
        self._register_resources_check_inherits (mapper) 
        self.api_extension_manager.map (self._register_controllers) 
missing_core_extensions = self.get_missing_core_extensions (self.loaded_extension_info.get_extensions ().keys ()) 
    if ((not self.init_only) and missing_core_extensions) : 
       ...
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is Python program to compute API.
missing_core_extensions