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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_plugins():
 """ Load all availabe plugins. Returns ------- plugin_cls : dict mapping from plugin names to plugin classes """

        plugin_cls = {}
        for entry_point in pkg_resources.iter_entry_points('docker_interface.plugins'):
            cls = entry_point.load()
            assert cls.COMMANDS is not None, \
                "plugin '%s' does not define its commands" % entry_point.name
            assert cls.ORDER is not None, \
                "plugin '%s' does not define its priority" % entry_point.name
            plugin_cls[entry_point.name] = cls
        return plugin_cls