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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 register(cls):
 """ Register variable handling in YAML """

        if not cls.IS_LOADED:
            cls.IS_LOADED = True

            yaml.add_constructor('!param', Parameter.parameter_constructor, Loader=yaml.SafeLoader)
            yaml.add_constructor('!env', EnvironmentVariable.parameter_constructor, Loader=yaml.SafeLoader)