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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 set_map_alpha(alpha):
 """ Alpha color of the map tiles :param alpha: int between 0 and 255. 0 is completely dark, 255 is full brightness """

    if alpha < 0 or alpha > 255:
        raise Exception('invalid alpha '  + str(alpha))
    _global_config.map_alpha = alpha