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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 command(self, cmd, progress_hook=None, *args, **kwargs):
 """ Execute a model command. :param cmd: Name of the command. :param progress_hook: A function to which progress updates are passed. """

        cmds = cmd.split(None, 1)  # split commands and simulations
        sim_names = cmds[1:]  # simulations
        if not sim_names:
            sim_names = self.cmd_layer.reg.iterkeys()
        for sim_name in sim_names:
            sim_cmd = getattr(self.cmd_layer.reg[sim_name], cmd)
            sim_cmd(self, progress_hook=progress_hook, *args, **kwargs)