def __create_context(self, main_root):
		context_dir = os.path.join(main_root, 'context')
		safe_mkdir(context_dir)

		action_default = {}
		for unit, param in self.__task.data['workflow'].items():
			action_default[unit] = self.__action_mgr.default_config(param['type'])

		navigators = self.__config_mgr.navigator()
		context_format = self.__navigator_mgr.context_format(navigators)

		self.__context_mgr.create_context_file(self.__task.data, action_default, context_format, context_dir)
def union(matches, root, cwd):
    """Union a list of matchers.

    If the list is empty, return nevermatcher.
    If the list only contains one non-None value, return that matcher.
    Otherwise return a union matcher.
    """
    matches = list(filter(None, matches))
    if len(matches) == 0:
        return nevermatcher(root, cwd)
    elif len(matches) == 1:
        return matches[0]
    else:
        return unionmatcher(matches)