def actions_for_category(category):
    """
    Returns set of actions containing each group passed in.
    
    Param:
        category must be in {'Permissions', 'List', 'Read', 'Write'}
    
    Returns:
        set of matching actions
    """
    actions = set()
    for action, action_category in _action_categories.items():
        if action_category == category:
           actions.add(action)
    return actions