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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def load_sub_plugins_from_str(cls, plugins_str):
 """ Load plugin classes based on column separated list of plugin names. Returns dict with plugin name as key and class as value. """

        plugin_classes = {}
        if plugins_str:
            for plugin_name in plugins_str.split(":"):
                pc = load_plugin(plugin_name, MONITOR_DEFAULT_PLUGIN_MODULE)
                plugin_classes[plugin_name] = pc
        return plugin_classes